This MIGHT work?
I ran a search on heat vs fiberglass. Seems the car guys use various spray/roll/brush methods to put down various products that reduce noise and heat. I ordered enough of one product that will cover at least 2 cowlings, so I rolled on 2 layers of the stuff on my top cowl to see if did it work. I have been kept on the ground (rain) so I have not yet tested this stuff. I will say it sure does apply easily with a 4” roller, and smells like latex house paint.
I’ll have a report for you when I can get off the ground!
The bottom cowl is covered like Dan’s with a peel n stick heat resistant product from one of the car suppliers, so it is doing fine. If this other stuff sticks and reduces the heat on the top, I’ll roll on some of it where the fiberglass is bare on the bottom cowl. Maybe this product will help with keeping the inside of the cowl a bit cleaner...