You'll want header paint from an automotive store. BBQ paint isn't up to the task. I suggest you scrape or burn off the paint around the burners you have already painted on or else the high heat paint will serve no purpose other than to be burned with the rest the first time it's fired.
The plan right now is to and a burner grill to the trays. Here is an updated photo of the project. Thanks for the tips about paint. I will probably strip the pair off the trays and get a high temp alternative before we fire it up.