How do you "polish" a dustcover?

I use wet or dry very fine sandpaper and depending on how deeply it is scratched, I start with 400 grit and keep going all the way to 1500 grit and use water. Then I use swirl mark remover for automobile paint and a buffer or polishing pads. It is a lot of work but works very well.

Novus #1 plastic polish and cleaner, found at Harley Davidson stores.

Second the Novus aslo found at some glass shops