Re: Which is the best camper van/ Class B RV for winter camping?
We have limited experience (Jan-Feb 2011), but here's our take on it: Yes, it is doable. We have an 09/10 Roadtrek C190P, and used it in moderate sub-freezing weather (high teens to low twenties for several days). We drained the exterior/outside fresh water tank, and used the interior/inside fresh water tank and the hot water tank (can't fathom why they tell you to bypass the hot water tank: using it keeps it from freezing and warms the surrounding water lines). Whenever we drained the gray and black tanks, we put a gallon of antifreeze plus a gallon of Geo-method mixture (water,Calgon, & dish-washing soap) in each (obviously, other chemicals could be substituted in the tanks, but we like "green"). If the gray tank gets filled more than half way (it rarely does as we mostly use the campground showers), we dump in another gallon of antifreeze, and as the weather gets colder, you might want to do two gallons in each tank initially rather than one. I don't know if makes other than Roadtrek have the inside tank, and that would be a showstopper without it in our opinion.
Traps: If you do use the shower, you need to dump some antifreeze down the trap afterwards, as the shower trap is under the floor and is subject to freezing. The kitchen and bathroom sink traps are inside the cabin on ours, so aren't a problem if the cabin is kept warm. The other trap that most don't think about is the hose on the macerator. The hose from the pump runs uphill through the transmission crossmember before going to it's storage bin. All this will contain whatever you last pumped through it, and could freeze. After dumping, we add the antifreeze to both tanks and pump each again until we get antifreeze coming out, so the macerator and hose is protected "full strength". If you have another make of camper, YMMV on all this.
We found the windows around the "bedroom area" to be chilly, and jury-rigged some blankets there in addition to the curtains. Marti has made some insulated pads to go there for the coming season. We like being out in fall-winter-spring because it is a lot less crowded!
One other point: In snow/freezing rain conditions, this stuff will melt off the roof and sides of the van (and you can see the spots that they were sloppy about the insulation!), and especially on the windshield and windows. There is a Chevy (not Roadtrek) problem that this water will run down the windshield into the heater plenum (the grill at the bottom of the windshield) where the water is drained down the front door posts past the hinges. It freezes there, and eventually you can't open the door. Some water also drains down the rear door posts/hinges, and can hinder opening the rear doors. The "fix" is to break this stuff out of there (using a broomstick or similar) before it gets real bad.
Good luck, Dick & Marti Tillinger Allegany NY