I agree, the E-Flex is great for the Kickr. Not sure it can fit with his needs, but the small footprint and fact that it is actually 2 separate sections may allow use without the limit that seems his concern.
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Thanks - It does look great, but…$$$$$ and I’m in the UK so no option anyway 
I’ll check out Chads DIY options and see what I can find.
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Thanks Chad - AGAIN!!
Lots of food for thought here - my key need is simply to improve comfort for those longer rides. I don’t plan on spending hours but 2 be able to do 2hrs in comfort during periods of bad weather would be a huge win. I like the idea of possible DIY options as I don’t want to throw money at it ideally.
I’ll check out your links and no doubt be back with more questions in time as well 
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Here are some quick pics and description of the next step I need to take to finish it.
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The main device is a simple plate that supports the Neo with a minimal footprint that matches the Neo.
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The underside includes two simple casters. They function as the lateral rocking pivot axis, and they also allow fore-aft motion.
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The missing piece is a simple extension that will start at the back side of the front section and extend to become the foundation at the rear (red rectangle). From there, install a section of cut pipe (like PVC) that serves as the “track” for the casters on the trainer support (yellow arcs and lines).
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That system relies on the fore-aft centering from the front section springs, as well as the steering and lean control from the front as well. My hack is serving the same purpose as the regular E-Flex Kickr version, but I am just removing the centering since that is already present at the front.
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In essence, this could be done with any other trainer that isn’t a Kickr. Exact height from the casters and track with it’s connecting support, needs be high enough to allow the width of the deck to not contact in a lean earlier than the rider wants. I have done some rough setup and think I have it right, but need to finish the build to confirm actual function.
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Does this design not need the inflatable balls?
The stock E-Flex does not need inflatables. It uses pure steering for lean control.
This hacked Neo version would also not need inflatables, and would still be steer to lean.
But my other, very heavily modified version does use inflatables, because I have a hybrid system that uses steering and leverage controls to lean.
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I’ve just ordered some rubber dampers and m10 countersunk bolts. The dampers are 50x50mm and from a quick Google a tennis ball is ~65mm? Do I need to space the boards apart? Is there an optimum amount of pre-compression?
How are people retaining the tennis balls?
I am not a huge fan of the tennis balls, but can offer some info related to them. Most people drill a hole (unsure of size) in one or both decks to hold them in position.
As to the spacing, it depends a bit on how much lean angle you want at max. From memory, you need around 3" [75mm] inner gap between the decks for 7* lean per side, if you are around 32" wide. Smaller gaps do work and have been done plenty, but will lead to an earlier lean limit.
For those with the 50mm tall mounts, you can use additional plywood discs or similar spacers to widen the deck spacing. Certainly something that you can play with over time.
As to the pre-compression, yes, that is a good idea. I have a lengthy video that I have wanted to shoot on that concept. But in short, some compression of the springs on both sides when level is good. What is best is actually a case where the leveling springs are still engaged on the open side, even at full lean. It goes to the feel at the center and when you flip-flop from one side over to the other.
Without pre-compression (or preload in typical spring discussion), you end up with a more pronounced “toggle” between the directions. It can feel “supportive” to users new to rockers, but it feels just plain wrong to me. I used foam blocks for years, that did include preload, but came loose and disengaged at full lean. The result is that toggle feel.
Once I swapped to 4" or larger inflatables, and the springs stayed fully engaged at all angles, the feel became so much better. It is more natural and smooth between each direction change. There are many ways to set these up and any is worth a test. Let me know as you get something functional and any feedback you have. I may have suggestions depending on what you feel and like vs don’t like.
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Perfect thanks!
I’m not committed to tennis balls, i just haven’t found an affordable inflatable option. I guess they can just be double-sided taped to the bottom plate? Or would you cut a hole for them too?
I don’t like cutting holes, so if I was to use tennis balls, I’d get some of those furniture cups and screw one to each half of the deck, at each ball location.
Are you in the US or UK? I can show you some possible options for inflatables to order.
New Zealand. I don’t mind ordering online, just some of the options were looking pricey.
I’ve just searched on AliExpress, but I don’t know if that’s a bad idea?
https://a.aliexpress.com/_mOxQfR2
I don’t like those yoga or balance balls/pods at all. The wall thickness is very stiff and not a great feel IMO.
Best to search for dodge ball, or any other inflatable ball from 4" [100mm] up to 8" [200mm], and mini inflatable balls.
Great thanks!!
So if I went for 5", or for you with your 7" ones, does that mean you have the boards 4"-6" apart?
No, regardless of the ball size, the 3" [75mm] gap is all you ever need for deck gap.
The difference on the ball sizes comes down to the options for placement between the deck, and the pressure within. Larger balls need less pressure for the same effective support.
You just insert the balls between the deck with minimal inflation (really floppy bit some air in them) and then inflate to final pressure once inserted. The extra size allows them to expand and reach between the decks for the best overall feel. So, keep that same max gap, and tune the feel with pressure.
I like the 5-6" range and think the 7-8" is also great. When in doubt, larger is usually better.
Ah perfect. The 5" ones are a quarter the price of shipping so I’ll try them.
Thanks so much!!
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Just to close the loop, I’ve ordered one of the Pedivella Rocca rear only setups. It seems to be very well made and offer exactly what I need with a small footprint at reasonable outlay. I looked at building something but frankly for the money its not really worth my time really.
I’ll do a novice review when it arrives if thats helpful for anyone?
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Right on! For sure, please share your experience once you get it. I am happy to read any reviews from new and old users. Congrats and I hope it gives you the comfort you want 
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I did my first ride - 2 hour z2 @ 60% - yesterday with my Stages SB20 on the Pedivella (photo below), after inflating the damping balls to around 8psi. Even 8psi felt too low at the start - a lot of bouncing - so I kept adding air till I got to around 9 or 10psi, and that felt better. After this first ride, I’m not sold yet on this setup versus using the SB20 on its own. The motion feels slightly off, which could be do to the fact that the SB20 is so solid and heavy, that it isn’t a good match to a rocker plate. But I also might need to tweak my setup - primarily seat tilt - slightly. I’ve spent a lot of time tweaking the saddle tilt to get it “perfect” for the SB20 sitting on the floor, and it just feels like its off slightly.
My comparison for how a rocker plate “should” feel is the InsideRide Kickr E-Flex, and one of the biggest differences in feel is that the SB20 on the Pedivella feels like its motion isn’t as “precise”. That is, any motion feels more exaggerated on the SB20, which I put down to its weight - it weighs just slightly less than I do. Pushing the damping balls further out - closer to the edges - could help.
I’m going to do several more rides before I make a final decision on keeping this setup or going back to just the SB20 by itself.
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I just did another ride, and after upping the pressure to ~11psi, I’m liking the feel of this setup more. The stiffer damping from the higher pressure significantly reduced the exaggerated movement I experienced yesterday, so the movement when pedaling is more subtle, and feels more natural.
If my wife is okay with this setup, I will probably tweak the pressure a bit, but keep it.
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I have only had time to skim, but a reminder to try the wider placement at the edges if you want max support and lower pressure. Sounds like that is a good change to start and you can change if you want more motion later.