I was petrified on the first test drive but the salesman actually did a good job of calming me down and offering helpful driving tips. We went out on the highway for a few miles then back on wide residential streets. I was so pleased to have gotten it back in one piece I bought it! Still in my barn 30,000 miles later!
When you go out, check out the blind spots. Some MHs have the side mounted cameras that help. Check out accelleration and how the transmission shifts as your build up speed - smooth or jerky? Braking, do you feel pulling right or left? Transmission or Exhaust braking - this is a big one if you spend time in the mountains. How she handles in crosswind is a big one also but very hard to test especially when not loaded down. In fact, if you're going to be driving more than one, consider bringing a check-list with you of things to check - not just for the test drive, bur of all the things you'd want in a rig!