I listed this reply in another section but I think it belongs here too.
Personally, I'd feel much more comfortable cutting the bottom of the storage space in the motorhome to accommodate the BBQ tank than modifying the tanks to be able to refill them.
I have a 1989 Dolphin. When I got it the propane tank was missing and a new tank was more than I wanted to spend. I modified the compartment so that a BBQ type tank would fit standing upright. Does anyone know why the manufacturers don't just use these tanks.