Mr. s. Why gelcoat? I would think a good paint would be much easier to work with. Maybe wood grain?
Having seen Mr. i's comment I was thinking KiwiGrip as well. Heck, almost anything with texture or that could be textured could be used. Truck bed liner?
One of the problems I could foresee with gelcoat or paint is that any glossiness would show any bump or seam.