I finally found the easy way to unload brush from my 5x8. Lay one or two pieces of rope in across the trailer so they will be under the load. the most important one is a foot or two from the back. leave enough on each side to toss over the load and cinch it up. I leave the tailgate OFF and cut the brush around 10 feet, overhanging the back a couple of feet. I will pull the load down using the tie down points and some ratchet straps several times to compress it and get more on.
At the end, I cinch the two cross ropes around the load, NOTE: these are not connected to any part of the trailer, just around the load. This pulls the brush in away from sides so it will slide out easily.
My trailer tilts, which is why I leave the brush longer than the trailer. When I tilt it, the weight is resting on the ground. My kids and I can pull a huge brush load out a couple of feet using the rear lasso, then tilt the trailer and drive off. Two 80 pound boys standing on the back of the load resting on the ground will hold it as it slide off the trailer.
Tongue weight is a bit of an issue with the load overhanging, if I had to go on the highway, I would not overhang as I pretty much end up with zero tongue weight. The method works without the overhang as well.....
Used to take me 30 hard minutes to unload, now 5 easy ones.