Ed, regarding your small PT issue, you'll find this forum is generally big on a cliquish attitude about the right way to do things (based on a few longer term members - again generally - who have an interest in maintaining the proper pecking order or are stuck on their form of experience), but if you hang in there you'll get an acceptable amount of willingness to support your decisions, as well as some answers to questions.
Since you're new, and it seems new to the TC thing, you'll find your use of common sense thinking "outside the box" will generate both admiration and condemnation (if ever so slight).
I have used PT in a few parts of my restoration. I chose against the marine plywood for my entire exterior plywood replacement process, mostly due to unnecessary cost for stuff I was painting anyway (paint on camper plywood is another example of "non-normalcy"). I wanted that "old lodge painted for protection" look on my build, and I'm getting it too!
My floor was 1/2" plywood with lengthwise 2x2 supports beneath (lots of rot). I rebuilt the floor with a new PT 2x2 (cut and ripped from larger dimension lumber) floor framing sandwiched between two 1/2" PT plywood surfaces, along with 1.5" of foam board insulation in the cavities. I also plan to run side to side some PT deck boards as three or four supports in the truck bed (fastened to the camper - I know, I could have just laid them in the truck bed).
As I recall, I haven't needed (my mind) PT above that floor level, but if I lived in a wet area I would really consider it for wings and below, or perhaps the marine for those flat panels. Sounds like you are familiar enough with PT to realize its drying, warping and twisting characteristics. Keeping it flat and weighted until install, and then fastened in ways to keep it straight should answer those concerns as it dries out.
It was at about that point in my rebuild where there was a contingent here who began stepping back from much support for me, but there was always that interested group who helped keep my reporting mostly worthwhile. 'Course they're step back might also have something to do with my step up and shut them down sort of method that I'm generally willing and able to throw out there too.
Other tinker thinkers like us sometimes just disappear from here (and the long term neanderthals think we just failed on our projects and went away). Some of us hang more in the wings. Do your own thing. I'd suggest you just ignore some comments, although I admit I cannot do so. ;)
Best to you!