We have a little shower tent from Wal-mart that has held up well. It looks like this.

We heat water in a pot on the stove and pour it into one of those solar shower bags because they never get very hot in the sun.

This setup is cheap and effective, but takes a while and is no fun in the dark. On rides that bring us back to camp after dark we're usually trading cooking duty for showers in the RV of our regular camping friends.
We will beg for showers no more!
I ordered a Triton 5L hot water on demand system and am setting out to make a compact-ish carrier to hold a propane tank and house the pump, heating unit, hoses, and provide a place to set shower items. Stay tuned.
Triton 5L unit
