I never could figure out what and why that strip or piece of paper/wood was used for next to the door on a tr3. I first thought it was a nailing strip, but why a nailer--- most all the other vinyl is screwed to the sheet metal with cup washers? Was it to make a finish weld on the B side?Plus that little piece of stuff is basically floating in this odd shaped channel, so it is not structural. Then I thought the stuff is “oakum,” and when oakum gets wet it swells up and seals. I remember my dad showing me that when I was a kid with pluming, now putting that striped piece of cardboard in that little channel makes senses; it is an oakum door seal, Genius.