Two-Tone Layering Question

Whichever way you do it, it takes a lot of clear to cover a line. If by urethane you mean a (hopefully high quality) single stage then there isn't much you can do. 3m makes blue and green stripe tape "fine line tape" they call it. Enables the cleanest straightest lines. And as far as the holes go please weld them in. You'll be happier in the long run. Even if you were to epoxy from the back it will eventually fail. Best of luck in your adventure!