Some ideas for your consideration:
1. Tank heaters http://www.ultraheat.com/tank_heaters.html
These use significant electricity, however.
2. If you're going to be spending most of your daytime at school you won't be able to tend to a woodstove. Perhaps a combination of central forced-air RV furnace and woodstove. Furnace for daytime to keep the interior above freezing and woodstove to really crank up the heat and save propane when you're in the bus at night.
3. Consider an auxillary freshwater tank inside the heat envelope interior for winter use, since your water needs will be limited if you'll be showering at the gym. Leave the exterior freshwater tank empty.
4. A cup of rock salt added to your grey or black tank after each draining will reduce the wastewater's freezing temperature by several degrees.
5. If you install a forced-air furnace, you can build an insulated enclosure (with an airspace) around your undercarriage tanks, and route a furnace duct into the space. Make sure there's also a return duct. Bonus: If you position these between the chassis rails, the floor running down the center of your bus will be warmer in those spots.
6. Many highway rest areas have free sani-dump and freshwater refill stations. If there is one nearby your parking spot, regular trips to same will not only take care of wastewater disposal and freshwater resupply, but also help keep your engine in good condition and recharge your batteries via alternator.
7. Consider two small gensets vs. one large one. You'll save on genset fuel if you only run both when you have larger power requirements.
8. Cut Reflectix (foil backed bubblewrap) to fit your windows (and skylights) in as many layers as necessary for use at night. Attach with Velcro.
9. Skylights will suck heat more than windows of same size.
10. Try to find a parking spot with access to shore power. If you keep your power consumption low a regular extension cord should suffice.
11. If you can park near someone's house you may be able to use their plumbing also (only in above freezing temperatures) using a macerator pump such as this one with hose tying into their Y trap:
http://www.campingworld.com/shopping/it ... -kit/26125