Originally Posted by family wagon
. . . . The metal paths from inside to out will sink a lot of heat; with the metal skin inside the bus you'll enjoy the sensation of being enveloped in a tube of ice. Anything to block that radiant heat loss will be a big help. Do whatever you can to insulate on the inside to block that -- rigid foam board, foam camping mats, etc. Stay away from fibrous insulation like cellulose, fiberglass, etc because they'll be constantly emitting fibers into the air you're planning to breathe.
If you can orient the bus long axis east-west and make the insulation covering the south-side windows removable . . .
X2 on both. As far as insulation, trapped air is what blocks heat transfer. Ever been to a Home Show where the closed-cell spray foam guys have their little science project going that shows the air currents between the fiberglass strands, carrying heat from the warm side to the cool side? It will make you a believer in foam. (Cue the '60s hit by the Monkees.)
If you park so one long side is facing south, you not only have the maximum sun during the (short) winter days, you also are not taking the prevailing winds from the west broadside 24 hours a day.
The solar hot air collectors do work, I once was a member in a church (also in Upstate NY) that had the hot air collectors (Trombe Walls). Once the sun came out, they could bake you out of there if you hadn't set the shut-down limit to turn off the blowers.
One of the designs for hot air collectors on the internet, which may have been linked here, was to cut the tops and bottoms of soda cans off, join them into tubes (solder or duct tape I guess), paint them black, and put them behind a glass enclosure. Guess what? You live in a glass enclosure.
You could put columns of black soda cans, or cut lengths of black plastic well pipe, mounted vertical INSIDE the south-facing windows during the day. No need to open a window and make a wood-and-glass box outside. As the tubes heat up, the hot air flows out the top, sucking the colder air up from below. A fan can spread it around. But this really only saves a little firewood, as it only takes a few hours for everything to get cold again (maybe like around 6 PM on days when the sun goes down before 4:30).
So the best suggestions have been:
Insulate with closed-cell foam as much as possible, wherever possible
Cover over metal walls with ANYTHING that won't conduct heat away through the ribs to the outside.
Hang curtains or even better carpeting on the walls, floors, ceiling, and as dividers to keep the heat in the area being used.
Close off parts of the bus that won't be used.
And finally, lay in lots of firewood.