Support for larger TV

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.

Some "walls" in RV's are very thin plywood with a paper front and can be hollow, you might need to build a stronger mount behind the wall or in between or place a backing, or you might end with a big hole in the wall.

navegator

Countersink the bolts that hold the mount to a one by six board the length of the TV. Glue and screw that board to the wall. Figure out how you will hold the TV in place and incorporate that into this board before cutting it to length.