here in canada eh, we are not allowed to use an unvented propane heater indoors. the place i worked imported them(not knowing the laws)for resale. when they ran the ad, we were contacted by the powers that be, and told we could not even sell them, we finally cleared them out calling them greenhouse heaters.
there is so much moisture released as a by-product of the burn, i could not see them as good for any piece of metal, let alone a valueable hot rod. mike