I cannot see the framing or the windows or the roof holding up over time with use on the highway. There is a lot of bouncing and without proper reinforcement, a lot of potential for flexing.
A lot of this type of camper have been built over the years but placed on a flatbed truck so the bed was rigid and provided a "foundation" for the camper.
For simple get a used Six-Pac camper. Mine had no fridge, no furnace, no toilet or shower, but it was light enough to haul around on a Toyota 4WD mini truck with a tiny 135HP engine.
