I would call said people without her knowing about it and see if they would be ok with you coming up earlier. Explain to them that while its easier to set up than a series of tents, it still will take some time and effort on your part to do so.
Maybe this just hasn't been communicated to them correctly so they can understand. I can't see why they would have a problem with you showing up earlier than them, since you only need a place to park it and thats it.
My wife wouldn't suggest taking my truck and our trailer, even if I was riding along. If she did, and she had little to no experience, I would say no.
In your case, its damned if you do, damned if you don't. If you can't reason with the other family, then I say tell the wife that you guys aren't going and she can call them and explain it. The argument that ensues will be better that what will probably happen with the truck and trailer if you let her go it alone.
If she is adamant and is going to go it alone, then I think she should do everything alone in that respect. Hitch it up, pack it up, pick it up...etc etc. If she can do all that, well then go for it I guess. I would be staunch in that no one else drives it other than her, I'm not sure if insurance will cover it if something happens and its a friend driving.
My guess is that you both will be staying home, having an unpleasant weekend.
I'm like you though, too much work to go for only 1 day. Heck I get annoyed by leaving friday night and coming home sunday sometimes.
