Will, most trunk arms only open about 45 to 55 degrees. The best I know is the VW buss rear hatch. And yes, the roof is not strong enough to hold the door.
But now we have the mini Vans.

Gonna wind up using hinges like what you pictured, I need it dependable and don't have time to play with it, I want to drive it, not look at it on occasion. It's not a great deal having to duck rolling in, I'm doing it now and have been for 10 years, hopefully in time maybe I can come up with something different, but not important.

That's them. I came up with nearly the identical hinge. I didn't care if the hinge was visible like most seem to care about, my van has bid exposed hinges already, LOL!

Maybe one of those small, stationary type flip seats like in a UPS truck, etc... would serve the purpose?

Where does it mount first, the van or the door, and how do you mark it's location?