[Cobranut]

One thing to consider when deciding whether to spend the dough for those aluminum interior walls: You can't screw tiedowns into the aluminum skin.
With the plywood, you can mount loops anywhere you want to tie down spare parts.
I have stuff strapped nearly all the way around the walls in my trailer.
Keep in mind, the really heavy stuff, like the tool chest, needs to be bolted into the wall studs, but light stuff can be screwed anywhere.

Just a thought,