Rick, you should be able to hit most repeaters on low power. The rule of thumb is to always try low power and then use high power if you NEED to. Your antenna is the most important part of your signal.
For RF radiation, mounting on the roof is the best but we're not cranking out the most dangerous frequencies at high power while on 2m and 440. That being said, all of my transmitting antennas are on my roof. It was easy to install multiple antennas, it's the best ground plane, and I know I don't have to worry about adding RF exposure to my 5 year old daughter.
As for CB or ham, there is no question about ham being the best out on the trail. It's great wheeling with other hams and not having to deal with the problems you get with CB. But, as Specter said in the first post, more off roaders have CBs then ham so you are more likely to find help if you have both. I'd recommend having 2m and CB on the trail if you go with single band radios. Of course, a multiband ham and a CB is better. I actually enjoy having CB when I'm in traffic so I can listen to the truckers talk about what lanes are blocked and alternate routes. I find that their info is still better than my smart phone's.
