I,m upgrading the deck fitt's on the big Sorcerer. (cleats and fairleads) and as per usual on many 70's fibreglass boats - no pads under the deck to spread the load. When I was younger (and slimmer) , I would use big s/s penny washers on either ply or hardwood, - laminated to the underside of the hull (but nowadays laying on my back in the confines of a speedboat hull are out of the question)
I had to cut the grp footrest in order to remove the fuel tank (which was obviously bonded in after the tank was fitted) - and fuel tank had to come out :-
1 - in order to gain access to the rusty old (3" long) coach bolts that had been used to secure original deck hardware
2 - to change all the tank fittings and hoses (remember that old plastic stuff with a nylon weave inside that went brittle on your old BSA Bantam fuel line?) - this boat had it as the main fuel line 15ft of 1/4" to the engine (no tap! no filter! - the breather and the filler hoses, and it also sported a leaky drain tap in the bottom of the tank

I was considering using one of the modern outdoor "Grab" adhesives to bond the pads to the underside of the grp - just wondering if anyone else has gone down this route?
-your thoughts, if any, - welcome

Hiya, did the same with our latest boat last year but probably easier to get to. I used one inch thick hardwood, stainless fittings and a solvent based grab adhesive. still there 8 months of sea use later so am hopeful!!! Kgarla