I may have talked about this idea before but it was inspired when I was
doing blister repairs on a boat and used a heat gun. The heat gun
literally drove water from the hull and it poured out of adjacent
blisters so...........Why waste time heating the glass when you really
want to heat the water and other polar molecules. Enclose the boat in
a cover of aluminized plastic and put a microwave generator inside.
The water and other polar molecules in the gel coat would be driven out
over a few days. Of course you'd have to keep the power level low
enough to not cause arcing near any metal fittings but that should be
easy. You might want to score the gelcoat to facilitate the
evaporation of the water.
Next, you drive thermo-setting resin into the gel coat under pressure
or even slowly setting ultra-low viscosity epoxy. Finally a sealer
coat. No BS gel coat peeling that fails 80 % of the time.