Dwight...

I mounted my fuel tank as per the instructions, and there was still room to squeeze a little foam in, around, and underneath. I've had zero fuel foaming problems, and I did silicone the tank to the firewall. When I glued a stick of balsa across the inside of the fuse to hold the tank in, I put a small piece of foam between it and the back of the tank. If you need a little foam at odd hours, Wal-mart sells a dog-bone shaped car wash sponge (foam) for .99. Works great!

BTW, your gonna love this plane!