I used the rubber band method with no foam for the first season. As I was doing my winter maintenance, I noticed the vibration had started to wear on the tank. In my case, it was only a matter of time before the tank would have failed. Iam now in the process of moving my tank back (as well as a slightly larger tank, going from the stock 14oz to the Dubro 16oz tank) closer to the CG. There are many photos in this thread on mounting the fuel tank on the CG.

Here is a photo of the stock tank after 11 contest flights and 72 other flights plus 1 engine break-in on the ground. This was a very short season for me without a lot of practice or contests.



If you are set on mounting the tank in that former, I would suggest using wing saddle tape to cushion it a bit, or maybe 1/4 inch foam. Just know that it will probably wear away due to vibration.