Looks like a nice project with a good plan. Look forward to seeing the updates.
Here's a wild idea that I'll throw out!
What if you sealed up the rear door on the drivers side. Then have any passengers get in only through the "passenger" side?
Probably a crazy idea but I can't recall if I've ever seen one done that way.
...and since I've already tossed one hairbrain idea out there...here's another!
Why not make that working rear passenger door half the width? Similar to an "extended cab" truck. (Might look cool or it might look a bit too stretched out)
Just trying to think outside the "box"!