[Hotrodhornet]

I recently repaired an aux aluminum tank on one of my pick ups with fiber glass.  Cleaned tank real good with wire brush wheel on an electric drill.  Next painted area with resin, then applied fiber glass fabric, painted with resin, one more layer of fabric and resin.  After curing, painted the whole area.  Is still working 5-6 months out.  But on coach tanks, I might consider taking it to a welding shop & having a new bottom or at least a large patch welded over the leaking area.

Thats my plan. I only want to do this once.
I have also had to repair my waste tank , it was leaking where the anodes were installed. 
It you have the odor control anodes in the waste tank it is probably when and not if they will leak.
They are screwed into the tank into a plastic bung, eventually the anodes rust and expand enough to crack the bung.