I've done this using the method outlined above with good results. I built a custom cowl for my Cub with a detailed dummy engine. I painted over the gel coat with auto primer and rustoleum, but then I found some flaws in the surface that I wanted to fix. So 5 minutes with acetone and paper towels took it all back off to the gel coat. I figure it would have taken at least an hour to get it clean with sandpaper. The acetone cost about a dollar, so it's not exactly a big investment to make.