Brett,

I viewed your tank pictures. My opinion is you are doomed. Your time and money would be much better spent having a competent sheet metal shop make you a new tank. If you are 'weld-smart' and own a small MIG machine, you can have 16 or 18 gauge panels sheared and formed, then weld them together yourself. You can purchase weld flanges and install them where you want your pipe fittings to go. Your chances of a leak free tank are improved immensely when you start with new material and lap weld the seams. My two cents!

Stuart