The old Rovers used a tin sheet over the top of the roof with some ~1/2 to 3/4" spacers
as a heat shield, I would think that could help you too, and adding some insulation to
the inside would be good.
The extra tin on top is like a heat shield around a turbo, it stops the "microwaving" effect
of the heat that you will feel if you don't have it or good roof insulation.
Wild