Winnebago uses 1/8 Luan sandwiched with polystyrene foam then more Luan then fiberglass - maybe 1/16 thick fiberglass sheet. It is laminated together under pressure with huge rollers - whole wall at one time. Where they mount cabinets and other items they enclose steel or aluminum plates in the wall so the screws have something to screw into. The plates hold the weight.
There are aluminum rails top and bottom along with aluminum wall studs. You might be able to screw a big backing board to the top and bottom rails and any studs in the area to get the strength needed to support the TV.