A couple months ago, we took our RV out with all 5 of our yorkies!
We have a bumper pull, so yes, they were all hooked up in the truck; some in carseats, the others with the seatbelt thingy. All went pretty well, a couple of the older ones did escape one morning while pottying, but, fortunately, since they were the older ones, they stayed close and they did come right back. We hooked 2 ex-pens together for them to play in, and kept their harnesses on with ID at all times. Don't forget to bring along nutrical, pepto, benedryl and hydrogen peroxide incase you need to induce vomiting. Also, be sure to have their shot records; some places require them. As for sleeping, they pretty much slept where ever they wanted to; mostly on top of me!
Hope you have lots of fun!