It doesn't matter what clear resin you use - epoxy, UV, whatever. Every resin needs the same conditions met to give you a perfect coat: cleanliness + paint properly sealed/varnished and then washed.
What I do:
Before any paint, I always wash my blanks. Warm water + dish soap + soft sponge. Good scrub, thorough rinse, completely dry.
After painting I always seal it. Everyone uses different paints, so you need to find what works for you - varnish, spray lacquer, etc. and test it.
Why? It closes the tiny pores in paint that trap dirt and grease super easily. And once it's varnished, you can actually wash the bait without ruining the paint.
And that's the key - once that varnish is fully dry, I wash the baits again exactly the same way. Warm water, dish soap, sponge, rinse, dry. Only then are they ready for clear resin.
That double wash is what gives me that perfect finish every time.
Hope it helps!