I have plans afoot to construct true 4 season "RV type" full time living trailers/flatbed "truck camper" units.
I am working around my #1 design criteria for the day use living area: is there enough space to swing a cat?
No, sorry, there are no window flower boxes and falsie dormers...
or soaked insulation held in place by a "belly tarp"...
There is heat recovery ventilation, attention paid to weight and balance, efficient heating/cooling system, future maintenance...