Not sure if they used this but some manufacturers have used it over the years:
Butyl Rubber tape. It comes in black. Very sticky and stays pliable. I like the stuff and use it for other purposes like sealing wires going into the firewall etc...
It is very very sticky and hard to remove. You have to go slowly and carefully, so as not to scratch the sidewall. In the cold you need a heat gun or hair dryer.
A good trick to help get the remnants off the sidewall is to get a ball of it collected and use the sticky ball as a tool to push or roll on the bits still on the sidewall. the rubber will tend to stick to the ball and come off easier.
2011 Allegro 32CA \ 2013 CRV toad
Previous:2007 Winnebago Class C
99' Winnebago Adventurer /Towables