[Pipe_Dream]

Trust your nose! You can try to pressure test the tank without removing it, but it won't be 100% accurate because the foam or wood may mask any problems (see my gallery for pics of my tank, the worst hole was right under one of the wood strips that secure the tank in place). Like MJ said, remove the hatch and sniff. If you can, do it while you're filling the tank. If you smell any gas, you have a problem.