Hi Rob,

I usually wet sand it, however, it is very low loading (as is loading sand paper grit) and sand well dry as well. Wet sanding also makes it easier to see what you're doing because you can wipe it away where as dust clings. If you've primed it lightly and it looks good, don't sand it unless you're worried about weight. That said, a good work down with 400 grit will produce a good tooth for the color coats to adhere to.