Most powder coat masking issues are with the blasting portion, as it takes duct tape to be thick enough to withstand it.
My powder coater won't mask at all. I take care of it and he knocks it off the price.
OP's idea has merit, as my powder coater has told me that's the only way he'd do a two-tone: do the coating first, take it to the body shop next door for the paint and after-decal clear coat. By the time I added it up, it was not a bad idea, but generally, with an Ironman, you are only after one color, whatever is on the stays. In most cases, the ST/HT are fine, or good enough.
@
gugie, did you strip and prep the whole frame, then mask what you wanted masked, before bringing it to the powder coater? And did the powder coater then do whatever additional prep needed before spraying the powder?
The powder coaters I've talked to were uncomfortable with any tricky masking. No problem with threads and open tubes etc, but they didn't want to mess with lugs, contrasting panels, etc.
I was tempted to mask, sand and paint white panels over the fresh powder coat, but in the end elected not to. If you can clear coat over powder coat, you should be able to paint over it as well, no?