I have mounted some pretty heavy things on the thin RV walls using the backboard idea. I put up some 3/4-one inch back board using MOLLY BOLTS then you can mount things like TV MOUNTS or things like that using regular screws into the back board.
Putting up shelving should be ok following the same idea but you may have put up a grid first something like this. You have to spread the weight out across the thin RV walls for them to support anything real heavy. Maybe something like this first using MOLLY BOLTS then you can mount the assembled cabinets etc from LOWES to these using regular screws..
The pantry area next to the fridge in 213X is ideal for mount holders for sliding plastic tubs
The area inside this 12-inch wide shelve is open in the inside. Some versions have outside door access to this area.
Just keep looking for unused space and add some plastic tubs or more drawers etc.. The area behind and below the shirt ward is also open storage area...