Well, it turned out that the leakage was definitely coming right through the fibreglass. The pits on the roof were letting water through the shell. I peeled back the ensolite on the top of the cupboard and could see water drips forming from a particularly bright spot/pit.
So, here's what I've done:
- Filled all the pits with System Three Quikfair epoxy fairing compound.
- Put fibreglass over areas where the gelcoat had been worn through to the fibreglass underneath
- Decided to install a Maxxair fan in the roof so reinforced roof with 1/4" marine plywood epoxied to the roof. Before doing so, I used scissor jacks and some lumber to lift the central portion of the roof and create a bit of camber. After cutting out the old vent raised area, the plywood strips were weighted down when being epoxied in place.
- After the plywood had been faired and smoothed with more Quikfair I sanded the entire roof with 80 grit sandpaper and then laid down a layer of 2.3 oz fibreglass cloth with System Three Silvertip epoxy to laminate it to the roof.
- Cut out the 14 x 14 inch opening for the new fan
- Built a frame using douglas fir to raise the fan high enough that it didn't intrude into the trailer...flush with the ceiling inside.
- Epoxied and fibreglassed the frame into place
- sanded and faired everything on the roof and then started painting
...three coats of two part marine epoxy primer and 6 coats of two part polyurethane marine topcoat paint.
- installed the new fan with butyl caulking tape.