Like above, tried it before and the gelcoat weakened the vinyl making it soft and giving it some wrinkles...the curing of a mould can go up in temperatures till 70°C if thick lay up so this will soften the vinyl and glue as well... 
Like Hanaldo said above a PVA might make a barrierfilm to prevent the gelcoat softening the vinyl but heat will still be an issue...not saying it is impossible but take great care...I would personally rather go for the chemical release agent or pva straight on the hood and worst case you'll have to repaint the hood