Not sure if you mean me…
I used International Paints Pre Kote undercoat, the filler was a Plastic Padding Gelcoat Filler, which is a polyester resin based filler which sands down fairly easily. Go easy with the catalyst, especially in warm weather.
The trickiest part I find is filling pin holes. I don’t know if they were already there or whether my rubbing down of the original gelcoat has opened them up, but there’s hundreds of the little bu**ers!. The filler seems to get pushed out by air pressure as you try to knife it in, paint also does not want to fill them. Maybe the best way would be to open them up a little with a small drill bit.
First coat of the new finish today, dark blue International Brightside (discontinued – use Toplac from International). A litttle patchy but a very nice colour and deep shine. Apply the paint with a foam roller, then “tip” it with a foam Jenny brush. More photos next weekend.