As Martha said, we currently own a smaller Class C. And we've had a Toyota Class C and the VW Eurovan. The most important part to know before buying one, to my mind, is that every possible choice is a compromise in some way. The VW was wonderful, but it also dictated how we used it. You wouldn't want to spend a month in it without some breathing motel room intervals. When we stopped for the night on the road, every move by one person forced a corresponding move by the other. This gets old, especially on a rainy day when you aren't driving. They are great if you are very active, such as going out for walks in the rain. We primarily used it for destination travel to California some place nice and such, where we would stay with friends and or relatives. We ended up needing a motel room at least once/week. The nicest part for me was that it could be parked or driven anywhere a car can go, no worries about going downtown, etc. Plus, if Martha needed a break, we would pull over at the strip mall and she could walk around while I napped or snacked. MPG was about 20.
The Toyota Dolphin was a piece of crap junk, rocking and rolling and sqeaking whenever there was a cross wind, very tiring to drive. Mileage was about 10-13 MPG (V-6), not much better than our current Class C. But enjoyable to have a toilet and all the other niceties.
We bought the new one with the intention of staying out for extended periods in the boondocks, big fridge and freezer (I don't care what you say, travel food anyplace near the highway is not good by the second day), go hide and lounge room, and dogs on the lap. I can't stress enough how important that becomes on a long trip with weeks and weeks with the same person disagreeing with you about everything you do, even your jokes. I also like to stop every three or four days on the road and just putz and sit and watch TV in comfort. This was important to both of us.
It's best to figure out how you will use it, and your personality and activity type. If you're incredibly active a smaller VW or Sprinter chasis will be fine. Both get good mileage and fit just about anywhere. If you primarily will use it as a second car and for road trips to visit friends or sites, these two are good choices for two people. Before making the current choice, I thought the Sprinter would be fine as long as we maybe rented a room or efficency apt for the week when we got wherever we were going. 10 MPG more with a smaller one would also probably mean much greater local use. And it sure is nice to have a place to change clothes or just rest get away for a bit. By getting the larger one, we have been forced to drive the car to visit people about one hundred-two hundred miles away, 300 miles/10 mpg-30 gallons of gas @ $2.50=$75, which is about the price of a motel room. One of the most pleasant uses was having it at Disney World, where I would get sick to my stomach from too many people after about 4-5 hours. We could go back to the coach and cook and sit until round two started in the later afternoon. You can't do that without a motorhome; you have to sit in the bar and drink $4 beer until you're less frazzled.
As it is, travel can be pretty cheap except for the gas. When we are hard at it driving, we stop at truck stops, grocery stores, or Wal-Marts for free. We get there late and leave early. Most midwest campgrounds cost about $20-25/per nite. National parks and such can be much cheaper, especially if you stay longer. We stayed at a campground in Mississippi on the Natchez Trace for two nites for , I think, $12. Roughing it in the boonies without electricity or water can be free or almost free. We like the quiet and nature stuff. It's those danged highway campgrounds that suck up the money.
Start out by thinking about the primary use it will get. Those big tank Class As are fine, but you will have to worry about unscheduled stops or any strange adventure ideas, plus you almost always need to rent a car once you are settle down or tow one. If you are taking the kids with, think about just putting them in tent for the few nites they might travel with you. Don't buy a big one just for that one week in the summer with the family.
I suspect our next purchase, after about five years with our current model and doing the type of traveling we plan, will be a Sprinter chasis Class B. This will change the way we think about our travels and our behavior again. Or maybe not.