I haven't seen the shower upgrade posted for awhile and I thought some might be interested in what I did a few months ago.
I purchased 3 yards of this "Clear Marine Vinyl 12 Gauge Double Clear Polished Porch Enclosure 54 Inches Wide by Yard". This is the stuff that they make windows out of for canvas, pop-up campers.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
I attached it to the walls with Velcro. It works great but you have to clean the place where you attach the velcro with rubbing alcohol.
I made the left hand piece wide enough to cover the back wall (plus 4" on the right) and the left hand (folding) wall, all in one piece. That way, when we close down, I just leave that part in place and fold the wall. It helps if you put a bath towel over the back wall so that it goes between the folded surfaces. That keeps them from sticking together.
The right side wall, I cut to fit and attach with velcro across the top. I remove that piece when folding down and I roll it around a pool noodle and just leave it in the tub for storage. When I install this piece, The extra 4" that is added to the back wall, overlaps this piece to prevent water from passing between the sections.
We only need a single 3' wide shower curtain. For extra room, I weight the shower curtain down on top of the toilet for more shoulder room (I'm 6'2"). This set-up increases the useable space in the shower tremendously.