This year I switched to the Fiberglass propane tanks and posted my project to one of the three trailer boards (FGRV, and two Casita
boards). The tanks are a little larger in diameter, but all I had to do was split the plastic tanks cover and trim the bottom of both halves right at the point where they curved in about a half an inch. I used rivnuts to replace the pop rivets, and it worked perfectly! However, I did have to create a new tank clamp to hold the tanks on the tongue, because the loss of that 2 inch bottom of the cover made the cover top almost touching the top of the tanks.
I don't remember which board I posted my solution and photos on. One of the photos showed the modified tank clamp.