Fuel now days has an anti foaming agent in it and we no longer have a foaming problem so I just hard mount my tanks. For my 72 RX I have used everything from my old chest waders to the noodles you buy to drift around in the swimming pool. That's some really good foam and there are several ways to use it. Just slip the RX into the center hole. Works very well for the battery too. I have big sheets of open cell foam I have bought at the fabric store and use it to stuff things like fuel tanks that are up front in the fuse to keep them from shifting around. With the 2.4 RX I just hard mountg them too. I have built small crash boxes for them though and lined them with styra foam and the foam you buy at the hobby shop. Inside the box when you buy a new engine there is sometimes a hard closed cell foam that I use for things too. When I go into craft or hardware stores I put my mind into airplane mode and just look around, there are tons of things you can use.