Many paintshops will tell you they are experienced in spraying fibre glass.........but just think about it. 'Any Spray Shop' does your paint job in say, the summer........the car goes through winter OK 'cos you haven't wanted to take your nice fresh paintwork out in the nasty cold and wet weather........summer comes and you do a few shows and the next winter comes on and you use the car a bit, put it back in the garage and the following summer after a scorching hot day out a couple of weeks later you see micro blisters on your five grand paint job. You're gonna take it back to the painter arn't you? - and there lies the problem - he will most likely tell you to get stuffed "its 18 months since I did your paint job mate, you are well out of warranty"
Unlike metal glass fibre (and filler) will absorb moisture - so if the paint shop uses the same prep techniques for 'glass bodied cars if using the same wet sanding processes they'll need to make sure any absorbed moisture is dried off in an oven? - am I wrong fella's? - and there lies the cause.