Pat,
We use seatbelt material. We cover it with the same material that the interior of the car is trimmed with (leather or vynal) and sandwitch it between two aluminium plates at both ends. The outside aluminium panel we stretch the alumnium to cup the strap on three sides (covers the rough edges). The straps are secured to the steel plates behind the dash sides and the other side is secured to the door.
These straps will stretch so should allow the door only to open slightly less than the 90 degrees.
I hope this helps, give me a call if I can be of any further help,
Best wishes,
Robert