what to use to seal inside of doors behind door panel?

Home Depot sells 4mil poly sheets pretty cheap. I sprung for the "good stuff" and bought the 6mil stuff. Its in the paint dept.
I attached it to the doors/quarters with double sided tape.
Do you have the original pieces to use as a template? If not, you can make one of each out of cardboard, then trace it onto the poly film. The old rope caulk is usually visible on the door so you'll be able to reproduce it that way without the original pieces.
Keep in mind that along the bottom of the door or quarter, there is a slot cut into the sheetmetal that this poly film is supposed to slip into in order to channel the rainwater back into the door so it doesn't enter the car.
I think a 10'X25' roll of film is about $14 or so.
Hope this helps.

George