Ok, this may be an odd question but as this is sprinter #2 for you I was just wondering if you have ever considered not using the side sliding door of the sprinter for access and relying on the rear only for access?
Yeah, I've thought about it . . oh . . . endlessly.
For starters, the slider is a pain in the butt compared to a regular door, hard to work and damn noisy when you have to shut it at 11:30 in a crowded campground. One of the best (and guttiest) mods made on a Sprinter was to weld the slider closed and cut a section out of it which then got hinged to operate as a regular door. Given that's too advanced for most of us, it's common (did it on our first one) to limit the travel of the slider by putting a block in the slider track. Unless you're loading palettes, half the door travel will be more than enough to leave. So in the first Sprinter, the back half of the slider opening was taken up with a floor to ceiling cabinet that had the refrigerator and toilet storage and a foldup counter.
In the first van, we made a conscious decision to give up cabinet space to get lots of windows, and that was a borderline good decision since, because of the permanent bed, shallow overhead cabinets, and the space devoted to the mechanical room, we were low on interior storage. It was OK, though, just not great. In the new van, we have bigger overhead cabinets, that whole storage space over the cab seats, and more drawer space. So I think we probably have 50% more storage, which was possible because of not having the valuable rear accessible storage and a permanent bed. One of those, "can't have everything" things.
The current layout is in response to a special consideration of mine . . . when I was doing the prototyping, I fell in love with the ability to sit on the sofa and open up the slider and look out. Particularly when you're someplace like on a beach, orienting that big slider to the view and just sitting there looking out was fantastic. It produced a very open feeling with lots of ventilation, and so that face-out-the-door slider was a key element put into my final design. But I don't know that I'd recommend the layout for general use, since that view-from-the-sofa thing won't be important for very many people. (Most people would just say to take camp chairs and sit on the beach, though you, more than most, can sympathize with the idea that you might want to look at a February Oregon beach without actually sitting on it.)
In a serial production Sprinter RV, because of their enclosed bathrooms, the big window walls are gone anyway. It also doesn't help that far-and-away the easiest windows to put in a new model Sprinter just have little slider openings at the bottom which give almost no airflow. But all of them still use the slider to get you in and out. But I did give a lot of thought to using just the rear door--the curbside one is the one that opens from inside first--and think the idea has merit. I saw three downsides, though. First, it's a long way down to the ground, so you need some intermediate step thing, and the step bumpers they make may or may work well for the people using it (it's still a big step). Second, most campground spaces are oriented for people getting out of the side, so you'd find it more awkward getting the food to the picnic table, etc. But those are small points; the third issue is more of a problem--you need a "hallway" that's probably three feet square just inside the door. That nine square feet is in a prime location and it'll take clever design (pull the toilet into it; use it for the bottom half of a fold-out bed, something) to keep it from being nine square feet of 24/7 wasted space (you only have about seventy in a Sprinter to begin with.)
So I encourage you to try to design something with the slider blocked, but I suspect you'll find it most straightforward to cut the slider travel in half and then build as much floor-to-ceiling stuff as you can stand. (FWIW, nothing keeps you from putting hatches in the roof for ventilation and light; you'd want a higher quality item than I used, but it was a slick setup.)
