That sounds like something you could easily build, using one of the $9.99 ez up screens that I just found online...
cut out one of the zipper sides to fit the inside of your door, add some velcro*to*the*sides*to hold it*up and voila! instant screen door that you can remove easily, like the uhaul
screen! I think the way we plan to set up our ez up screen shelter, we will need only 3 sides to be solid, then the 4th side that would be against the trailer can be cut, using the section in the middle w/ the zipper to cover the door, and then*some how attach the 2 cut sides of the big ez up screen to the camper (velcro maybe?) Sounds easy enough in theory.*
*I will give it a go, and see how it works out. I already have the screen ordered, and if it looks good, I might go ahead and order a few extras. At that price, if I mess it up the first try, it's got 2 sides with zippers, so I can afford to make mistakes with this project!
Thanks for the ideas!