For those who might want even a cheaper solution, go to this web site for wireless cameras. They are intended as surveillance systems but there is no reason they willnot work with a small TV that can operate off your truck's twelve volts and has a video input. The cxameras are meant to be used outside, etc. so they should stand up I am going to try one.
I also found a mirror that gets attached to your existing mirrors at Pep Boys for under $20.00. It is installed and seems to work fine, but not very big.
This is the site for the wirelss cameras.
http://www.x10.com/products/x10_vk45...d34#dd535.443c