Ahh, I hadn't even thought of dropping bar soap through the floor! That's something to keep in mind when we build ours. Of course, we could always use liquid soap ;)
My husband has been working on an island off the Maine coast, which is all off-grid. Outdoor showers are common out there. I know...
I've seen people put a water storage container (like a trash can, often painted black) on support beams above the shower. A hose attachment and gravity does the rest.
My concern with the coiled hose idea is that the water would be blazing hot after sitting in direct sun for any length of time...