Paint sanding question

Good info Oldman! I use blocks but I probably should switch to a hard board near those lines. Thanks.

To onemeanA: I'm going to shoot with an initial coat of epoxy. I always sand that with 400 grit, then apply a skim coat of filler where I need it, then more epoxy and sand once again. I know we all go about it differently but that's how I do it.