I should have taken a sequence of pics to explain it better, however, it's basically a lever style ramp. Run the sled up the length of the ramp which gives you enough leverage to lift the whole thing and slide it into the bed.
I've used a piece of osb to protect the bottom of the truck bed. I built the ramp rails out of 2x1 rectangle tube, rungs are 1x1 square 10ga. 10' x 46" with some cut bed liner plastic for runners.
Can you build it better, stronger, faster, more reliable etc? Indeed, but not for $130. That's my entire investment.