Make your mind up, it will either work, or not.
you need to draw the gas of the top of an auto gas tank and not the liquid from the bottom of the tank
the oulet fitting on an auto gas tank has a dip pipe that go,s down into the liquid
on a vehicle the liquid is drawn of and go,s down the feed/gas pipe to the vapourisor under the bonne/in engine bay its then vapourised and drawn or injected into the engine (well thats it in basics)
what you need in a propane gas heater is the gas and NOT THE LIQUID. (you can get a fitting to fit to an auto gas tank to draw of the gas from the top of the tank but of course the tank needs to be empty and safe in order to fit the valve fitting
been there and done it when equiping council vehicles many years ago ..