Last summer I spent WEEKS working solidly on a fibreglass racecar body, I used paint stripper to get the 7 layers of thick paint off.
If you do choose to use paint stripper be careful not to leave it on for a long amount of time, it will eventually eat into the gel coat, and fray the fibreglass.
If that happens dont panic, the original fibreglass can be saved using a few layers of resin and some woven fibreglass.
Take time and make sure you apply as many layers of resin, bondo, filler, and primer that you can before paint!
good luck, and wear a mask!