You mentioned in your intro that you have two small kiddos… assuming you are camping with them, I might suggest lowering the platform for better vertical space, and you can relocate the cooler as needed… could go at their feet while sleeping, which still allows you full leg room, or just put it on the roof at night. Personally, I like the idea of resting the platform on the wheel wells, and it can be secured with bolts from 3rd row seating
Another easy thing with the current platform would be changing the mattress. There are plenty of comfortable sleeping pads these days, and you can enhance them by laying a yoga-mat-like material below. That would save you probably half a foot of vertical. Even cheap department store foam pads are decent.
How temporary is the setup? Would make sense to keep 2nd row seating for the kids, but it’s easy to remove, and would clear up a good amount of space for this purpose
If I were in that position, I’d be planning a platform that slides out of the way in order to use 2nd row seats while traveling. You could also take out only one side of the seat... better storage + keep 2 legal seatbelts for the kids. Hinge that portion of wood, perhaps? Like a “seat lid”
Rest assured, they will surely appreciate how cool it was to grow up camping in an 80 series with their mom