Your best bet is clean and dewax the hull, then sand it.
You want to dewax before sanding otherwise the wax gets pushed into the gel and the epoxy won't adhere properly.
You really don't need to paint at all based on how you will be using it. If you feel the need anyway then by all means it needs to be a hard paint that will last up to a) being dried out, and b) the rolling on and off the trailer.
Lessons learned are opportunities earned.