I can recommend this one..
http://www.campmor.com/webapp/wcs/stores/servlet/BannerManager?adv=670226&prod=49412

Essentially a 'dry bag' setup as a sun shower..
much nicer than any others that I've ever used,
since you can open it wide up and let it *dry out*

(which helps keep fungi and other funkness from growing in it)

Also have and used one of these..

http://www.zodi.com/

although you have
to be careful.. the water can get superheated and
one can burn themselves very easily.. I recommened
firing it up, recirculating the h2o for a while until warm
then shutting off the flame.

Get a nice rubber make (fold/rollup) to put down on the
ground (to stand on)  with holes so the water drains through.

as for privacy.. well I suppose one could rig some sort of curtain
from the liftgate (my idea that I've been thinking about)

or just go off in the woods somewhere..

hth.

  -tim