If it is a single day trip (or maybe even a weekend trip if rare), I say explain to her why it is important to you, sign up and do it. Then offer to support her in something she finds important / enjoyable. I mean what is the other option - never doing things that are important to you because of fear of negativity.
Disclaimer: I have been divorced 27 times.
I am not saying this is the only way to make a family work. She is part of the family. The family comes first. Kids are different. Kids WILL put parents first (periodically). Putting the family first will let you get what you need.
Though I could be wrong. I have been before. I will be again.
My wife is a marriage and family studies major, and highly recommends this book. It might come in handy to many of those struggling in here 
(hint it’s rarely your spouse’s fault, but with the right techniques and time you can have a marriage with trust and love, and you’ll be able to do so many things you want)
