I have the LP6500 in my fiver, last April I was boondocking at the NASCAR race in Richmond and used 5 of the 40# bottles..
I mounted 2 brackets on the wall inside my basement, I then placed each tank inside a milk crate to keep it better stabilized. I hooked up a 2" ratchet strap to each bracket and ratcheted them tight against the wall..
Once in Richmond, I filled them at the local Costco, then used them and took home the empty bottles.
Not the best solution for boondocking, but it worked... We were able to run the 15k ac's from Friday Am to Monday AM..