Re: wheel wells:
I cut out the bench seat pivots and stamped reinforcing ribs from the inside of the wheel well when the moisture started to leak in on rainy days. They had rusted beyond repair. I replaced the resulting hole with a 12 gauge plate and 1/2" x 1/8" thick angle iron taped with bolt holes for the seat pivot (I reused the top pivot post retainers) and triple fiberglassed the wheel well side. These repairs (both sides) are still rust-free four years later.
I also sandblasted the super-rusty tack welded laminations where the bottom edges of the wheel wells come together with the pan and inner sides and fiberglassed the whole area (around the edge as much as I could)--rust is starting to reappear there after four years including some thick stuff trapped between the layers.
I must've spent 10 hours removing as many layers of rusted metal there as I could, but the rust still prevailed.
The outer, visible circumference of the wheel wells also starting to rust through at the skin but the extra thick fiberglass on the inside of the wells seems to be solid enough to reblast and fill.
I took the rear bed walls apart and filled as much fiberglass in from the top of the wells as I could. If I had to do it again I'd mix some plain resin in with the chopped strand fiberglass to allow it to flow into the deeper crevices.