Sorry to ask...if one tank is not properly secured,,,why would 2 tanks then be properly secured? Maybe I'm not really understanding here, but what I'm reading is your having a problem with a tank moving, or being fastened in the correct place? It would be to your advantage to secure what you have, rather then deal with issues of having 2 tanks now to bounce around. If crutches or foam are needed in fusalage, build/cut to accomodate. There is always a way... good luck.