Haven't used the Valspar paint, but a few things to keep in mind, does the boat set in the water for periods of time(2-3 days at a time) trailered or stored on a rack? These things will say a lot as to how the paint holds up. As far as prep, you will want to get the bottom paint off( recommend soda blasting, had my 19-6 done a month ago and it was done in 6 hours, saved a bunch of time) you will need to de-wax the gelcoat then sand with at least 120 grit if not a little harsher, depending on the paint manufacturer recommendations. Just finished giving mine 3 coats of Pettit epoxy primer and 2 coats of Pettit bottom paint(epoxy).