A solar shower looks like this:
It's basically a bag with one black side, one clear side, and a nozzle. You
leave it in the sun clear side up, the sun heats the water, you hang it up
Me, I prefer my propane shower
(if I shower at all) because
I can shower after dinner. The solar shower has cooled down too much
by then to be comfortable.
The simplest shower platform/graywater evap system might be four 2x4s
arranged in a square with some sort of black plastic draped over them to
form a catch basin. A wooden pallet (the kind you see in Costco under
the loads of toilet paper) sits in the middle and you stand on top of that
to shower. Water runs through the slats into the evap pond.
But there are tons of other ways to do it. If it's just me, I stand in a
cement mixing tub that doubles as a catch basin/evap pond. If it's not
dry by the next time I shower, oh well.