Oh wow. I wouldn't go. Actually, I'd be re-evaluating the entire relationship (!) but I'm also not in a relationship, so take that with a grain of salt.

I don't think you're being unreasonable at all. In fact, I think you're being super reasonable - you've suggested a few things that would make you more comfortable, and he's putting his family's happiness (I assume, unless he really wants to spend all this time with them himself?) over yours. That would be a bad sign for me...

I get not wanting to make a fuss or be too demanding, but I don't think it's unreasonable to want to keep the trip short, or to stay in a hotel so that you have some space/privacy, or to take a little time for just the two of you to do something special. And, I think it's absolutely RIDICULOUS for him to "volunteer" you to cook a special dish for the family (that you don't even want to see!!!) that's going to require you to shop, transport cooking tools, and work. You're not his personal servant or chef!

So, again, I'm bad at relationships and not in one... but what I'd expect in a good relationship would be for you guys to discuss the issue, figure out a compromise that you can both live with, and then for him to follow through (i.e. not to go behind your back and make plans that negate your agreement - that is just so wrong!) It doesn't seem like he's willing/able to do any of that.

To be honest, I'd totally bail. I'm trying to get to a point of more honesty about my stuff, so I might tell him something like, "I thought you understood how much I didn't want to go on this trip, and I thought we'd come to an agreement about how we could organize things so that we'd both get a little of what we wanted, and neither of us are miserable. It sounds like you've committed me to things with your family that I'm not willing to do. I think it would be best if you go alone, enjoy spending time with your family, and I'll stay here and enjoy the holiday with my family."

But in reality, what I'm more likely to do is make up an excuse ("I feel like I'm getting sick, I don't think I want to risk 7 hours in the car... why don't you just go and have fun.")

Sorry you're going through this. It sounds crazy-making. Holidays seem to bring out all the crazy in families -- Good luck!