A-body door moisture barrier

I have made my own door panels, but never considered (until now) that I would need moisture barriers. Can anyone advise how to do it and what materials to use? Maybe some pics?

Thanks

What the material? Hot wax works on both cardboard/chipboard,plywood and mdf.

How would you spread out hot wax?

Brush or bondo scraper. Why not use the plastic sheet like the factory.

I would do that, if I knew what to use. Would it be like the kind used in home insulation?

i always thought the factory used rope calk [or as some call it, "dumdum"] in either black or white, which you can get at the [most] local hardware store. later on, they used a cloth type black tape that was super sticky. think cloth electrical tape. i don't know when that was phased in. possibly mid to late 70's ?
smarter people than me would know for sure.

What was the plastic like? Sort of like the kind used in home insulation?

4 or 6 ml plastic will work be fine. Cut the plastic a little inside of the door panel but leave it an inch or so long on the bottom. Secure along the top and 2 sides with strip caulk or strip butyl and tuck the extra inch into the slot on the bottom of the door and then cover the slot with gaffers tape. Be careful not to cover the door panel holes with the caulking.