I was wondering how many people have used bed liner as a head liner?

It should seal well and might not look too bad but wondering how much if any sound proofing the factory liner.

The other thing I can think of would this effect the heating or cooling of the interior?

 

you mean spraying the bare metal or the Factory headliner? Bare metal go for it, the actual head liner I wouldn't because of he moisture. it will probably weaken and destroy iy.

 

I was thinking about spraying (maybe brushing it on) the metal top but after checking some more I fear it would get too hot in the summer time.

I did see where a few people are putting bed liner on the foam headliner and that isn't a bad idea, just that my headline isn't in the best shape so would have to repair it first.