setting one up wouldn't be to hard but gettin it to mount on ur car would be a problem.. cause all you have to have is...
wiper, motor, gears
now you need to find a place to drill a hole for the shaft to go through into the car which has the gear at the end of the shaft (in the car) that mounts to the motor (in the car). and doing it on the window is not something u want to do.. if you see SUV's and how they have the flat glass on the back, they can run the shaft right under the glass on the door part and there would be a motor between the metal part outside and the panel inside.. which has the wiring running up (probably not very hard to do but lots of time and patience)
http://auto.howstuffworks.com/wiper1.htm
you could probably cut out the top (the rear windshield) of ur trunk into like a small triangle and have ur wiper go down into the trunk thru that little hole and have the motor in ur trunk. but then you have to have a way to keep the rain/snow from getting into your trunk