You will probably need to drill small holes for the prongs on the T nuts, as they don't penetrate fiberglass
very well. That said, I like them and am using a lot on my boat: low profile on the overhead, and totally leakproof if you glass them over on the bottom. If it weren't for the possibility of freezing weather
you wouldn't even need to caulk the fitting (the hatch
in your case would of course need some caulk). If you drill out the screw holes oversize and fill with epoxy
, then re-drill to size, you will have a totally waterproof installation
. I see only two drawbacks. The installation
of the T nuts and epoxy filling the holes is time consuming and tedious, especially if you have a lot of them. You also need to be careful not to cross-thread the screws once the T nuts are installed; they seem to be a little easier to get a bad start than regular nuts, perhaps because the threads are rolled, not cut. I even tested one for pull out strength and it passed (the deck
had some serious flex but the T nut was holding just fine).