I had a little bit of an epiphany.
I played with the questionable notion of blocking the entire side double door, instead of just the side that can't be opened unless the main one is opened first (don't have a sliding door).
The design allowed me to put the kitchen unit and bathroom unit both on the door side, so plumbing won't have to be on both sides of the van, and also allowed the other side to be take up lengthwise by a cot-width sort of sofa, so if I don't feel like setting up the dinette bed thing to have something wider, I can just flop with no effort.
The kitchen has to be on the side where the door is, because those are the only cargo space windows (one on each of the double doors) that can be opened for ventilation (they have clamps and sort of push out at an angle). With the bathroom on that side, next to the kitchen, I would also have the second of those windows to provide ventilation for it too (kind of want the potty area to be fully enclosed, thinking I'd have to put an extra vent on the roof just for the BR - this design means I'll only have to put in one).
The epiphany came when I realized that I could go in and out of the side door by way of the bathroom, because it's not a counter, cabinet, or furniture. This would be especially helpful when it's raining or I'm filthy, not wanting to track rain and dirt through the van.
To summarize, putting these units in front of both of the double doors, does a few good things. 1. Bathroom and kitchen on same side = keeping water stuff in one place/share gray water container; 2. Bathroom has its own ventilation without me adding an extra hole on the roof; 3. Bathroom serves as a mudroom to prevent tracking of rain and dirt through the van; 4. Kitchen will still be by a window for ventilation; 5. Kitchen will still be accessible from outside; 6. Easy access to fill/empty water containers that serve both the bathroom and the kitchen; 7. can re-think my toilet option since access will be easier; 8. giving consideration to the drainage of water from the bathroom - I wasnt liking the idea of putting a hole in the floor for a drain to use much water in the bathroom, but with bathroom having door to outside, if I'm in a situation where I can let water go onto pavement, with no people watching, I can just let water go out the door... there is that step thing at the doorway, conveniently providing a downward path.
Aside from all of that, I'm wondering if I should put a sort of sliding door wall in front of the rear doors, for the purpose of temperature control.
Any thoughts on all of this?