Our camping situation makes the small trailer shower unnecessary also. I've added light duty shelving to 2 ea. showers now. For one I used cleat boards to rest nylon covered wire shelves upon. The other corner type shower I needed to also use some vertical supports down to the floor.
The shelves made the space much more efficient for stowing things. No longer is it necessary to remove half the stuff to access something.
I just used 2 ea. fasteners per cleat board. Should the shelves/cleat boards ever need to be removed my plan is to install hinged plastic button covers with stainless steel screws and sealant. I figure the covered screws will almost look OEM. The screw covers are available in various colors from Home Depot.
I used those covers when I removed the basically useless fold down bedroom TV shelf. Removed the shelf, re-installed the mounting screws with button covers, and installed a coat hook bar above on the wall. The coat hooks are much more useful than the always folded down never used, but often bumped into TV shelf.
In both showers it is easy to just remove the wire shelves and use the shower if needed. In one case the shelves have a lip on each side to hold the shelf in place over the cleat board. The other I needed to use a single cable tie on each shelf to maintain proper position on the cleat board supports.