Primer for Fiberglass Cowl
Sorry, that wasn't clear from your post.
I don't think the ceramic component would be an issue. It almost has to be reasonably sandable, and I doubt that you could cover the cowl heavily enough to add substantial weight.
Rereading your post I'd also suggest that you test the primer on something first to make sure it really is fuel proof. Does this guy know you were talking about fuel containing Nitromethane?
Dennis-