As with the interior, the next part is just hard work, filling in any screwholes/dings, and then sanding sanding sanding. Using 40 or 60 grade glass paper is fine for this, as the epoxy primer/undercoat has good filling capabilities.
A mask is essential – now is not the time to develop an epoxy allergy 
Hot noisy work
Once the finish is acceptable, give it a good hoover and a wipe down with a tack rag or three. Then the lower rubbing strake is masked off with Frog tape ready for painting with epoxy primer
Masking off ready for painting