I remember considering a "glind" (http://www.glind.com.au) when I was
setting up a 4WD camper for a trip into the Australian Outback. It attaches
to the cooling system of the car (sorry aircooleds!).

I ended just using a cheap shower pump & handset from a camping store. I
made an arm which I could attach to the spare tire (which was bolted onto
the back of the camper). I'd boil some water, pour into a bucket, add cold
to get the right temp, dump in the pump and I was away! Worked well.

My solution can be seen at http://members.ozemail.com.au/~jules/camper-v2/

> I remember seeing a picture of a home-made shower that was attached to the
> front of a bay westy. Anyone seen this one?