On the way back from work, I paused to visit Radio Shack and the Dollar Store. In Radio Shack, I picked up some 8AA battery holders. I figure 8 AA batteries should keep my fan working for about 12 hours. In the dollar store, I picked up a pack of 8 AA batteries.
Putting the new battery pack on the fan was almost simple. I could not rely upon a simple magnet to hold the battery pack in place. The pack was too heavy so I just moved a few things around and balanced it all in place.
Running the fan for several hours produced interesting readings. It seems not to be a simple process of sucking hot air out. Mind, one fan alone probably wasn't even tickling the problem. Two, when I install the second fan, might be much more effective. Failing that, I could get 4 inch fans to replace my 90mm (3.5 inch) fans.
I haven't done a diagram of the bus interior but it's layed out in the following order... Cockpit, galley,bathroom, bedroom, closet. The fans are installed in the closet. The bedroom is better insulated than any other part of the bus.
One of the interesting things that I noticed is that the vent at the back makes quite a roaring noise. Putting my hands near it, I could feel quite a breeze. Clearly I'm on the right track. I definitely need to install the second fan and possibly to get the correct sized fans too.