this blog entry by a certified child passenger safety tech has some useful points to consider regarding RVs and kids who still use car seats:
Here's an excerpt from the article that I found to be rather eye-opening:
"I would so love RVing to be the easy answer, but it’s not. Load up some food, throw the dog and kids in and go. If you got tired mid-trip, you laid on a bed and slept; if you got hungry, you made a sandwich. That’s the way it used to be before we got smart. I remember it being that way when I went RVing in the 70s with my dad and his family in the ol’ Winnebago. Unfortunately, there are some serious safety issues with RVs because of unrestrained passengers who can fly into each other in a crash (you’re 4 times more likely to be thrown from a vehicle if you’re unrestrained). A 40 lbs. child becomes a 2200 lbs. bullet in a 55 mph crash when he’s not buckled, so while it’s fun to run around and be free in the RV, it’s incredibly dangerous. And don’t forget about the luggage and other miscellaneous things laying around the cabin of the RV.
After we got all the logistics figured out, the RV was going to be $129/day + $0.32/mile + a fee to empty the tanks + gas + a per hour charge for the generator, if used. Insurance is included. In order to take possession, we would be required to pick up the afternoon before we needed it and return it the morning after returning home, thus incurring 2 extra days’ charges. Dh decided to find a nicer condo to rent for cheaper instead. "