My class C has the underframe winch holder for the spare. I think it's about the best all-around way to carry one if you can manage; it's not the most convenient to access, but it doesn't cut down on storage space or get in the way of a trailer or sit exposed to UV light etc.
I had to use it less than a week ago in the Great Smokey Mountains National Park, in fact. Changing a tire is not fun, of course, but not exceptionally difficult on a class C either. (In case you're wondering, I got slightly too close to a stump in a tight spot on Cades Cove Road, a spot made tighter because of a long line of cars pulled off the other side of the road. A few splinters of wood from the stump got worked in between the tire bead and the wheel's rim...luckily, the tire and wheel themselves appear to be uninjured, though I need to take it to a tire shop to have the splinters removed and things checked out.)
