You are definitely talking about a lot of hard, heavy work. To make the walls sturdier and thicker, remove the strip between the panels on the wall. Fill in the long open space between the panels with joint compound. Fill, dry and sand. Now you can attach wood paneling on top of the walls and paint it or leave it like it is. Or....you can hang the thinnest dry wall on top of the old walls. Finish off drywall and paint or put up wall paper or vinyl wall covering. Like I said, it's a lot of heavy hard work. My directions are merely a summary of how you can refinish the walls in your mobile home. Good luck with your endevours.
Have you thought about a new outside cover?Looks like wood panels vertically , can be painted any color or left original, insulates well, and cuts down on outside noise, definitely sturdy up the side walls. Have you checked for termites? Just a though...
11/32” Sheer Plywood will do this without removing and replacing framing. This is assuming your top & bottom plates are securely attached to the ceiling & floor.
If not, then angle brackets will need to be installed and that’s another set of details.
Simpson A35’s would be better, IMO.
Then you have to choose if you want to extend window & doors’ sills & casing in the inside or the outside.
Inside also includes extending the electrical boxes, which means getting an electrician involved.
Outside, Exterior glue plywood is required and is typically called CDX, x for exterior.
Youll want to screw in the plywood, on every stud.
To improve insulation? Outside put on foam panels then some.other kind of siding?