So, I think I'm going to give this a test run. My current plan is to use 5 inch hoses, and put the vents near the cabinets. The supply would be near the roof in front of my cabinets, the return would be below the cabinets near the foot of the bed. For my test run, I'm building my "plenum" from cardboard and duct tape. I picked 5 inch hoses because of this chart.
https://resaveguide.lbl.gov/step-6-duct-designI searched on line, and on high, the A/C unit should put out about 120CFM. The 5 inch hose is capable of 125CFM if the run is under 20ft long ( an elbow =15 ft) 4 inch won't get above 80 cfm and that's only a 3 ft run).
My plan would be to have the supply hose come off the top of the plenum, and the return out the front like yours. Then if I put the A/C unit on a temporary shelf over the fender, I should be able to have just one bend in each line.
For my test run I won't relocate the thermostat, just set it where I had it in my previous trips and put the system on high cool. I'll just unplug it if I want it off. This way I can modify the design of the plenum if I have any flow issues. If I like the setup I'll work on moving the thermostat.
Anyone see any issues with this plan?
Tom