If the surface below the load handler fabric was greased/oiled, it might do OK. I made my own version with a doubled over piece of tyvek house wrap inside a truck bed. It worked OK, but if I was working with dirt, it would build up in the corners of the truck bed and it would get a lot harder to slide/empty if any dirt got under the fabric.
I had better luck with a roll out type dumping bed when I wanted to move a load of fill dirt (I have an old backhoe). Picture a 6x8 "tub" sitting on a long sturdy frame (5x5 wood, well braced) sitting in the back of a truck bed. There are 2 casters on the bottom of the front of the rolling frame. There are 2 upside down rollers attached to the truck bed just inside the tail gate. I loaded the tub and drove to the dump site. On level ground, I opened the tail gate and removed the safety chains so that it would fold all the way downwards and then drove for 3 feet in reverse and slammed on the brakes. When you apply the brakes, the rolling tub keeps moving and tilts as it begins to fall out of the back of the truck. When it gets about 2/3rds out of the truck bed (about a 40 degree dump angle), a pair of chains/straps stop it from going any farther. I pulled forward a few more feet to finish dumping the load and then pushed/rolled the tub back into the truck bed and closed the tail gate. With this type of system, higher is better (more room for a better dump angle). You need some strips of metal to serve as "train tracks" to keep the tub rolling straight and you can't dump uphill or downhill (across the hill is OK).
Here are some pics. (it is very crude/not pretty)
