The PO of our '65 caravel
cut the rear bathroom in half. We fixed that and the endcaps with West Systems Epoxy. I've also used it for quite a few boat repairs -- it's the standard in the Marine Industry.
Here's one source
. I'd use:
206 Hardener (205 in cold weather)
Pump dispensers to get mix correct
410 microlite filler for non-structural areas
Fiberglass, if necessary for larger repairs. Use on back of endcap if possible.
Lots of good advice at the West Systems site