All new cars seem to use a thick clear plastic.  i have used a thick clear plastic vapor barrier on all my cars for the last 20 years,  worked well,  grab some "strip caulk" from the body supply store and run it around the perimeter just like factory.

cdnpont wrote:

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Good ideas guys. The one way Tyvek sounds interesting. Finding a small amount might be a challenge around here.

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 You can purchase it per foot, BUT it comes (I think) 8 feet wide!

the key is to tuck the bottom into the slot in the door, otherwise any moisture ends up in contact with the cardboard of your inner door panel

I agree with all the comments regarding heavy plastic, can't beat it when it comes to a vapor barrier. The point I would like to make, IMHO, is that it has to be sealed around the perimeter and ALL the window cranks and door handles, otherwise it is worthless. The other point I would to like to make IMHO about using plastic IS, when you go to apply your RUST CHECK product, you don't have to worry about the product weeping through paper based products to reach the newly covered door interior coverings. I used 3M black adhesive on our cars. I really did take much of an issue with the 85 GMC, plastic is there but not sealed as well. The reason is the door interiors are one piece Plastic.
I also agree with the Sound and heat barrier for the floors and firewall , I also used it to separate the trunk from the interior of the coach. Take your time putting it on and roll it out flat with no air locked in small spaces or gaps
Good luck with your project

Almost seems like it would be easier to attach the plastic to the back of the door panel.

Is anything on the market that is comparable to the original paper product? I have not seen anything but it would be nice to use a product that looks original. I'm interested as I will need this stuff soon for my 68 Impala. 

I wonder if an art supply shop would have paper like that.