Kind of like a rolling/tilt dump bed thing? How do you attach the tarp to the frame though?
I think that's my biggest quandary.. how to attach the tarp to anything with out it ripping.
I said Tarp but... thinking on it, a good piece of rubber would probably work better or chain mesh but there will be more to pick up after the fact.
Attaching to the front of the Skid... to me I would secure the rubber sheet to the outside of the frame, nothing to the bottom of the frame to interfere with the sliding. You would need a Strip of Metal, or Wood, to sandwich the rubber between the Frame and the strip; Hardware to mount the securing Strip should be Bolt-Through, with appropriate Flats and Lock Washers or Locking Nuts.
The height of the Skid can be anything you want or need within reason of the Trail Specs. Again the Pull should be designed to pull on the front panel of the skid, pulling from the rear can cause the unit to pull apart. Also, secure all corners with metal reenforcement.
Again, this is just a quick idea that popped in the old head, I am sure there are others that could refine the idea.
The Skid can be stored separately, leaned up against the barn or shop, can be handled with the tractor, and should slide inside of the trail confines without too much trouble... IF the lines of pull in the trailer are clear and relatively smooth.
What ever you do, good luck with the project !
p.s. I keep thinking on this but maybe no material floor, just the skid, to get the load off.
If you were to build one, try it out without a bottom, should work with some cleaning after the fact.