I was surprised you said this since you had a Turnbow–don’t they all have fiberglass roofs?
Exactly. I took a nap in my Brenderup on a 90+ degree day and it was cool in there. My Shadow with a 7’6" fiberglass roof is definitely cooler than the steel stock trailer (allegedly 7’ tall) that preceded it.
So I knew I wanted to have a fiberglass roof always, but the stock trailer was a friend’s who was selling when I found out my mare would NOT learn to self load in the B’up. But due to my first horse’s injury that would not have let him load in a step up, I knew I always wanted to have a ramp option. So after a while of owning 2 trailers, I ordered the Shadow with the best of both worlds, just in time to get one with a fiberglass roof.
If this interests the OP, the trailers I know of being made with fiberglass roofs are Hawk, Turnbow, Double D, Equispirit, Balanced Ride, Gore.