Hallmark will do flatbeds now, and also custom floor plans for minimal upcharge.
I did a ton of research, and all roads led to Hallmark.
We opted for the "mini" shower stall, but when you put the 365 PortaPotty in it, the 365 fits perfectly, and so the mini shower does double duty as toilet / mini shower (you just lift the 365 out, most likely carry it outside, and use the shower.)
We also got the AluCab Shower Cube, (outside) and Matt (hallmark) moved the outside shower to right by the Shower Cube, so that works beautifully!
I easily rigged up a privacy curtain, just forward of the mini shower... and there is a MaxxFan right above the minishower stall... so if there is another person in the Hallmark, and one person has some "serious business" to do in the PortAPotty.... then draw the curtain, turn the MaxxFan on HIGH, pulling air OUT of the Hallmark, and then no "emotional drama" to the adjacent person, sonically or smell wise.
and.... we have a 8' bed F350 gasser - with the tried and true 6.2 Gasser and the 2020 comes with the new 10 speed transmission... and we get about 12 mpg, at 70-75 MPH on the highway.... fully loaded. Very happy.
The F350 + Hallmark is just less than 9' high (even with the AC unit on the roof) and it is amazing in 25 MPH gusty crosswinds. Amazing.
Hope this helps.