You may want to try some of the low temp coverings that work for foam cores. Monokote needs a fairly high temp to properly seal down.

My 2 cents worth, I would paint them with Fusion, both main and detail colors and then top off with a Fusion clear coat. After fully drying, it is hot fuel proof, but drying takes a couple weeks at room temp. You can get a wide range of colors and the local ACE hardware stocks it, at least around me.

Don