[Espeefan]

Depending how are the Poly-Flex is to sand, I'd think about starting with something like 100, 150, or maybe 200 grit. The lighter grit paper just plugs up really fast. I've had really good luck wet sanding bodies. I do it in a sink (not the kitchen sink!) and fill a bowl or container with a soapy water mix. I rinse the paper now and then in the soapy water, and the body, under the faucet. Might take some time, but it will smooth over nicely.