Sounds like he has an A/C unit stuck in the front wall that overhangs part of the a-frame of the tongue.
No, don't hang your propane bottle from the wall. I doubt there is enough structure there to secure it. It probably wouldn't be too bad to put a couple of batteries on the back bumper if it's strong enough. If I were to do that, I'd mount one each where the bumper is welded to the frame. Weld up some small bases from 1" angle for the battery boxes to sit in and some way to secure them besides the nylon strap that comes with most battery boxes.
How about some pictures of your current setup?
