I have a 1978 Imperial Tri-hull 16ft and the color of this boat is like a metallic green. The sides of the boat are shinny the paint looks great, but the topside is another story. It is very dull and has no shine to it at all. I sprayed a shot of automotive polyurethane on it and it glistened and shined just like it was new. My question is, is this the gel-coat that is faded off of the paint? Can I use just the automotive poly to bring it back to a shine or should it require gel-coat?