I wouldn't hesitate to make a light ply brace for under or over the tank, or both, that makes the tank stay put some with the foam holding it. As for foam, I have been using the egg crate packing foam from shipping boxes for the tank and the radio, and battery holder. It is free, and cuts to whatever shape I need. Tape sticks well to it, so you can make a length and wrap it around, and use the tape to keep it together.