the industrial paint is probably a single stage paint. just reduce and spray. The clear, color, and hardener are all mixed in one. If this is the case, it won't absorb moisture. However it won't hurt to put down a couple coats of clear.

If it were me, Id put flattener in my clear and spray over the SS (single stage) paint. Just make sure the SS has enough time to flash, but not completely dry. If you put the clear under, you can let it dry, scuff it with scoth brite, then spray your SS. the only problem i can see is with your gloss flames on top. If your going to tape them, you need the color to be dry. But clear doesn't stick well to unscuffed paint. You can't scuff the SS without it showing through the clear. You'll have scuff marks all over your flames.

If you want the cheap route, go with the clear under the SS. If you want the better route, put some flattener in your clear. you can let the flat clear dry, tape off your flames, then spray your gloss over the clear with no scuff marks in your flames.

Good luck.