Those big tanks always rust out where they set on supports or at under straps usually at corners of tank. Keep that second one for a spare if you remove it. Even if you have holes in it, they can be fixed by the right welder. I get mine fixed for around $80 to $100 and he does a good job. Cheaper than new $400 tanks I see advertized.
One thing you can do is fill one tank, let it go down, fill other side next, use it, then back to orig side, see, back and forth. Both get used that way. The first time filling is gonna be the wallet breaker!
