Mornin, Fulltiming in that Jayco that long has no doubt already taught you some about full timing in an RV. I was in Maryville last year during the sub zero period in my Winnie. Everyone in the campground froze it seemed.
First point, on the 36' 5er, do you have a truck that can handle a 16,000 pound rig? Your talking one ton diesel territory.
You mention mid bunk, bunkhouse? second bed area? or did you mean something else? Loft? How many people do you need sleeping arrangements for? Mid bunk unit example
Grand Design As to brands, The upper tier Keystones, (Alpine, Avalanche Montana), are popular and generally well regarded, other brands offering comparable units are Jayco, KZ, Forest River, Heartland, Northwood, and Grand Design.
For starters, most mid tier units, and all upper end should have the enclosed underbelly, ducted heating, and heated tanks in some form. And in that size range, washer/drier prep is pretty standard.
Solar? how much? Panels can be installed on most any unit, solar prep is often so small in the wiring that it becomes useless for installation of anything more than a battery tender.
Res fridge, is an option on most rigs the size you are looking at.
Well insulated? there is only so much insulation in a 2 inch thick wall, four slides tend to make a unit even harder to heat and cool. What you may want to consider is if the units you are looking at have the ability to be used with at least a couple of the slides in. That flexibility could help once in a while.
Insulated double pane windows are available, at a cost. Cushions in the vent openings help too.
Hope some of this helps, happy hunting.