I would have to disagree on some Excel had a 0 degree guarantee (little good now) and Nuwa another orphan that used Dow blue foam in the walls. I used the same stuff in my basement and works well. And you left out New Horizon another good unit.
Most units are built as low cost vacation units to compete with other brands price point
Regardless how well insulated they are I think the windows and doors are the weak link. Excel was one of the few that used insulated access doors.
Nuwa in addition to the blue Dow foam had a attic or dead air space to deal with moisture that was vented.
Some of the older RV's were built very well such as Teton, Travel Supreme, Holiday Rambler Inperial.
