No need to remove the roughness if a plastic catalyst is used in the plastic prep, primer, and paint. The coats of all of that combined will give the cladding a smooth-look surface. Believe it or not, the rough texture will actually aid in the adherance of the paint.

I wish I could find fiberglass replacements of the cladding. I would paint it then. That Mooncraft stuff was damned sweet but too pricey and too far away.