there are two "main" tanks on my 1991....are you talking about the port side one under the settee....or the bow one under the vberth....
the vberth one is fairly easy to replace/repair....the port side one requires quite a bit of cabin rehab just to get to it, and even more gear moving to remove/replace
some on this site have cut access holes and made repairs, most removals involve cutting up the tank, or cutting up seat frames and liner stuff...
eianm here, IIRC, has some actual pics and information on these, perhaps when he gets settled somewhere, he will respond.
they are prone to pinholes and scaling...