Forget the 'marine' labeled strippers. I started with all that stuff and found a much better product and at a way cheaper price. Go to a Home Depot and get a gallon of 'Bix spray on'. It is the one that says ok for fiberglass (I think the orange can) and I used it on mine, no problem. $14.95 for a gallon and spray bottle. Put it on good and it will turn the paint to butter.
Hate to tell you, but you will be sanding to get it back to white which I'm sure is what you want since the surface will appear stained from the bottom paint. Have fun (do it while your still enthused about it!)
Any questions, let me know. I've spent a bunch of hours on this.
