I'm not fond of crates. I've seen too many people use them as an alternative to socializing and/or training their dogs - people coming over, just put the dog in the crate.
First and foremost, the RV and car should be connected to HAPPY experiences. Start with short trips going to the local park or natural areas. Let them get out and explore smells, etc. Make lots of short trips (less than 30 minutes). If you have to do a longer trip, stop every hour for 5 minutes. Let him step outside and go potty, etc., then get back in and start up again. Try to build up to big trips.
When in the RV, have one person sit in the back with the dog and get him to lay down - have the person pet him throughout the drive and comfort him.
Slow down! Many dogs get carsick. Taking curves and going up and down on non-flat roads at what we consider normal speeds can be too much for a dog's tummy. Slowing down reduces the sensations that a dog feels on the curves and hills.
Let the dog spend time in the RV when it's parked at the house. Have special toys/treats in it that are only for the RV. Make it a fun place in and of itself.