Getting the tank out is no problem. Get the trailer up on blocks and you will find it has a galvanized cover that is screwed on. Once removed it will drop out easily. Once out you can determine if it is repairable. Do yourself a favor before doing this though. Go under the sink and you will find 3 lines that go through the floor. You can see the top of the tank from there. Check to see if there is water on the top of the tank. We had a similar situation where we thought the tank was damaged. It turns out to have been a leak in the fittings behind the shower in the wet wall. If your trailer is a center bath like ours, this may be the problem. Airstream in its wisdom ran 3 lines under the floor on top of the tank. They used 3 elbows per line to contour the piping inside the wet wall. When we cut an access hole in the bottom cabinet under the microwave we found that 4 of the 9 elbows were leaking and one was cracked. The water runs down the line and on top of the tank so you don't see the leak inside. In either case the fix is not hard.
Dave & MJ
1988 32' Excella 1000 (Beauty)
1999 White Dodge SLT Laramie 3500 Dually, 4x4, 5spd, 5.9 CTD 235k+ (The Beast)