ive had my fiberglass vented bonnet painted on my car for 7 months,from carmate,and it has lasted great.
I heard the same as you have.That they yellow from the heat.the painter said that was a load of shit.And as long as the painter knows what he is doing you'll be ok.so far i have to say it is true.It even lasted a days driving in the new years day heat.LOL....
All i do,do is lift the bonnet when i get the car home and let it cool down.Some days.Kind of like a just in case thing.
IMO it will be fine.
Just be especially carefull where you put your weight on the bonnet.Cause it will crack/hairline crack the paint if pushed hard enough.