havent you ever watched into your boat
or a friends boat that has an inspection port its glass fiber then they put gelcoat
as paint and if u us lots of sanpaper one day you will notice your boat is turning yellow thats the glass fiber
Never mind 1200 it takes some serious sanding with 120 to get thru the gelcoat on a laser. (don't ask why I know this....) Anyways. To bring back the shine and depth associated with a nice gelcoat job try using a marine cutting paste and a variable speed buffer. I finish with a 2000 paste. Beautiful finish. Waxing? Wax melts and is a great place for tree fluff and other detritus to stick to.