I have the through-wall bolt mount spare tire mount, augmented with angle iron supports - they seem to have worked well for 30+ years (no cracks around where the bolts penetrate), so I'm going to redo it using neoprene-backed washers both sides of the fiberglass to seal it properly. I need longer bolts though, because the cool rims on the trailer are rather deep (I'm gonna keep them, as I have three of the rims and they look nice), and the tire presses very tightly (too tightly!) up against the fiberglass when it's mounted. So this will stand the tire an inch off the shell, allowing a tire cover to be put on.
As you can see from the pix, the through-bolts went right through the original carpet - I thought it had leather washers, the carpet chunks remaining are so gross! - and cracked the inner shell. I'll run the bolts through an aluminum backing plate for strength, and avoid the inner shell altogether. I'll patch the fiberglass, then the entire inner surround in the back will be lined with sheet cork glued to the shell (this will also cover all the horrible glue the PO used to glue carpet onto the walls!). I'll post pix when done.
Anyone experience leaks
with their through-wall bolts?