I doubt any manufacturer is using treated based on cost. Any normal stud wood material should be adequate.
As far as the walls...if they are laminated...per your post in the other thread, there probably won't be much, if any. Laminated walls generally don't have much in them except perhaps some for hung cabinets to attach to and around a perimeter. Think "surfboard"...that's what a laminated wall is. The laminated sandwich is the structure with very little else.
You might find this short read helpful for wall construction:
RV sidewall construction | RVwest
Do a search on RV Delamination Repair and you'll get all kind of returns that will provide you with a lot of information so you can choose wisely what you do next.
Here is a video from Keystone showing laminated wall construction. Actually, they have quite a bit of aluminum studs/supports in their sidewalls, but you'll still notice that it's not 16" on center or anything. I've been to Winnebago's motorhome facility in Iowa twice for tours. I'm amazed how little structural support metal is in their sidewalls. Around edges, windows, some plates for hanging cabinets, not much else. So it does vary from mfg to mfg.
Good luck! I wish you the best.