id probably do a test area first or take and cut a piece of sheet metal and then after it cures set it next to a heater to warm it up and check to make sure it isn't putting off any fumes and doesnt sag, remember this application is for exteriors that have the sun on them yes, but inside a vehicle in the heat stores heat inside the cab and can get much hotter with out the ability to release the stored energy (radiant heat) unlike on a roof. just a thought but do a tester first