Solar Furnace

[TygerCub]

You could put a row of those under the windows along the side of the bus and as long as that side is facing towards the sun, you'd be able to heat the bus pretty well.

Interesting idea.

Since the cans take up quite a bit of width, another idea may be to use either a half can (difficult to cut, though) or a row of copper tubing painted black. Shoot, for that matter, almost any thin walled tubing would work as long as it's: A) painted flat black, and B) covered by an air tight clear covering that traps the sun's heat in an insulating air pocket.

[TygerCub]

Another interesting thing that you can do if you plan to stay in any one spot for more than a day or two is to create a mini "green house" effect on the side of the bus. Using thin emt conduit and a thick greenhouse plastic, just create a lean-to over the sunny side windows. This will allow you to trap the warmer daytime air next to the bus as well as block any heat-stealing wind from the base.

Or, combine the two concepts.

The possibilities are endless, really.