We've owned a class A, 2 class C's, 2 fifth wheels, a converted school bus and a truck camper. We full timed for 9 years. I wrote for many RV publications and lectured at RV rallies. Might I throw out a few points to ponder?
1) I have known people who have full timed in a class C, a class B and even a truck camper. It all comes down to what your particular life style will be on the road.
2) A small class C gas model that sleeps 4 to 6 will be easier to sell than an older model class A. The C will probably hold its value a little better. A's are the fastest depreciating RVs on the road.
3) If you can manage the cost of the truck and a decent fifth wheel, that might be the way to go, especially if you first have to get a car that can be towed all 4 wheels down and pay for the base plate and hitch. They are not inexpensive! A pick up truck is easy to sell and a fifth wheel doesn't have an odometer. You will have only one motor vehicle on the road to insure, maintain and tag.
4)The cost of a Diesel pusher and the higher cost of Diesel fuel almost negates the couple of mpgs you'll gain. Unless you have a need to carry a heavy rig over big hills or have it loaded to the limit, you will be paying a premium for a Diesel pusher that you might not recoup. Let's not even talk about the high cost to maintain a Diesel Pusher motorhome. You can't take it to WalMart for an oil change. You have to get in line with commercial over-the-road trucks for service. Guess who gets taken care of first?
A C on a Ford or Chevy chassis can be serviced at any dealer just like a pick up, van or car.
5) Full time RVing is not the money-saving lifestyle it was several years ago. Consider finding some employment along your travels. Campgrounds are expensive. Public campgrounds are seasonal and those in warm weather areas are almost impossible to reserve. They aren't inexpensive, either. Be mindful that many state parks will charge a daily entrance fee on top of the camping fee.
6) All RVs are not suited to full timing. You will be carrying much more cargo than part-timers and it may be hard to find a gas powered motorhome that will hold all of your stuff safely. There is a big difference in the quality of construction in RVs. The little class A you are looking at might be just fine for weekends and small trips but it won't hold up to constant use and travel. The same goes for fifth wheels. You need to check carrying capacity limits on everything. an overweight RV will blow tires and it is just not safe.
You really need to take some time, do a lot of research and some critical thinking before you decide to become a full timer and definitely before you purchase an RV to do it in.
2011 Coachman Freelander 21QB