Here's a link to some pics of a nice sauna bus and other saunas for inspiration:
Erilaisia saunoja ennen ja nyt | Kuvagalleriat | Kaleva.fi
Pics 42 to 44 are of the bus. Pics 47, 48, 50, 52 have ice or snow saunas. Also don't miss the selection of tent, boat and trailer saunas.
Some choose to circumvent the heat and humidity problems with a bus sauna by towing a sauna trailer, personally I'd love a sauna harvester toad like this: