I might be missing the mark with my reply, but on our 16ft U-Haul VT, to keep the door open so only the screen is used, I just used a velcro strip on the body, and another on the door. Yesterday when I was loading the egg and making up the bed, I hadn't secured the door and the wind caught it - the velcro square took hold, and it never moved again until I closed it up for the night!
No holes in the FG and holds tight in the wind.
Are you saying you put one side of velcrow on door and other side on camper body? Makes since but on the rounded Egg trailers I dont think you can do that. Door wont open that far will it?
BUT.... I could see taking your suggestion and install velcrow strips over head on door and shell. Then attach velcrow straps to these once at the camp site to hold the door at your desired open width. Two straps with one leading from top outer door edge back to the shell toward the rear and the other toward the front. This would be adustable to hold the door at any desired angle. Very simple and like you say no screws. Assuming you get a quality bond of glue on the shell and door.