Well then.... new update... I've been going round and round on some design features, first with a 6" floor storage, then just a drop for the rifle case, then none... finally settled on gotta have it, and make it the height of my frame protuberance in the front that accommodates the tilt-trailer feature on my existing trailer.
Additionally, due to the tilt, not an A-frame tongue, and the low tongue-weight rating of my TV, I can't have a tongue box.
As such, the front portion of the "basement" will be that type of storage, such as battery, blocking, straps, dirty gear, etc.
The middle will be for steps for ingress-egress, camp chairs, awnings, side-tents, e-z-up tent, gear duffels, etc.
These 2 compartments will be access from the exterior with locking doors. (not in drawing)
The third section will access from the interior, and be for clothing, etc. that doesn't store in the bulkhead cabinets.
Additionally, the HVAC supply will pipe through the basement to the front, and the return will be in the rear of the cabin. I will have a roof-vent, and a start-gazer window, I just didn't put them in this design, as I spent too much time in 2.1,2.1, 2.2, 3.0,3.1,3.2 versions adding these, to then start over... lol
There is a swing-out section to the galley, that allows additional storage as well. and you can see the HVAC unit enclosure under the counter-top on the left side as well.