Leah,
It would probably work but leaves a texture finish that would be harder to clean. I'm not sure if a white is offered in that line but most things are available today. It is made for outdoor use and is a durable choice.
Frankly, the marine deck paint is formulated to go over gelcoat, it is made for harsh environment of sun and salt water and is expected to be walked on and take abuse. It is reflective, being bright white and walking on it from a grip point of view is like walking on the existing gel coat. I have not seen any difference. I do not know why anyone would want a thicker layer given the reason to coat the roof is just to stop chalking and preserve the gel coat. I worry about issues down the road when you want to refinish the surface. Multiple elastometric coatings would not be my choice, not sure about multiple coats of truck bed liner and what would be involved with that system. Bottom line, marine paints are some of the best paints made and formulated to do this job.
I have had the deck paint on my roof for 3 years and it shows no sign of any issues. If it came time to add a coat, it would be a light scuff, a solvent wipe and roll another coat on, but I may never need to do that...time will tell. I'm still a proponent of a thin smooth coating and let it shed the dirt and in the end will be easy to clean.
Later Ed
