I was looking at replacing my bathtub with a slightly wider, deeper
unit (32" wide over 30") - but space is so limited as is in the
bathroom that instead of taking up more floor space I was wondering
about going the other way and altering the wall behind the tub.
As I'd only need 2 inches more space and don't want to intrude into the
adjoining room, I was wondering if I could rebuild the wall other than
conventional stud construction - possibly turning the studs 90 degrees
so the framing thickness is 1-1/2" rather than 3-1/2", and to give it
more rigidity, instead of drywall, using 1/2" (marine) plywood instead
of wallboard on the tub side.
Is this a harebrained do-it-yourselfer's idea that would have
inspectors crying foul? I'd have to work out how it connects to the
rest of the framing, and it couldn't take an electrical box (and
there'd be no plumbing in that wall), but I've done enough structural
work on my house that I'd feel pretty confident in my work.

VMacek