The heater door is riveted to the firewall. The green streaks are car wax that is on the fire wall as a release agent for the (orange) RTV. The RTV is applied as a bead to the inside of the door and acts as a gasket to help keep hot air out of the cockpit in warm weather. Ironically, it was about -5 °C in my garage when I built this. (the propane torpedo warms it to about +5 °C). The door is being held in closed position by some duct tape while the RTV cures.
I found that there was a bit of “spring” to the door from the RTV on the side closest to the hinge. I ended up shaving down the thickness with an razor blade on a later step.