I'm currently in the process of replacing every piece of wood in my 16' tri-hull boat. While it is apart, I want to repaint the trailer anmd replace the bunk carpet to all match the new paint that will be on the boat. The trailer has a couple layers of spray paint uilt up. What is the most economicala nd effective way to get the surface reasonably paintable? SanPaper? What grit? Prime or not? The trailer will be painted with standard Rustoleum.