Geoff...
I didn't use a base coat, but in retrospect I probably would have used one coat of white out. As it is, I used probably 5 relatively thick coats of nail polish. Didn't even finish with a clear coat of standard nail polish. I usually wear the Infinity on my neck at night and never in my pocket, so there has been no wear on the coats that I did put on.
The LED and er... reflector? are recessed below the rim, so few things if any should come in contact with the paint. If they do, chances are high that your LED will get scratched too.
In going with the theme that the Infinity is a beater light, I really didn't take time to carefully work. I just used a toothpick to mix the recommended amount of glowpowder (IIRC, roughly a teaspoon for a near full standard size bottle of polish) and once it was mixed, I just used the brush that came with the nail polish. If there was any excess on the LED or an area that I didn't want to glow, I'd wait till it was a little dry, then remove it with the toothpick. As long as you paint evenly, go slow and let it dry between coats, you shouldn't have a problem.
If the stuff does come off, just reapply a little of the mix. Again, you might want to go with a white base but it does work well enough without it. My main reason to do this was so I could ID the light in the dark and it works well here.
Just remember that the glow powder particles are very small, but when it is mixed and spread out it will have a grainy, opaque appearance. Not very pretty in the daylight, but then again the Infinity isn't exactly a prom queen.
If you have any specific questions or need clarification, let me know. It's really that easy. That glow powder is VERY COOL stuff, but you have to be careful when working with it. It can get EVERYWHERE.
cheers