The Rover-Landers of BC

I have a 2002 Defender 110 Double Cab. I recently had to replace the weatherstripping on the back seat door glass. While doing so noticed rusty bits, to have a better look I removed the door card and the polyethylene liner. As I removed the poly liner I wondered why its there. Does the poly liner do any good? Is it advisable to keep it in place?

Hi, I think the poly liner is mostly there to prevent moisture and dust getting to places that it shouldn’t.
Best to reinstall it the best you can. If it rips, the red tuck-tape can be used to repair any rips.