The weight will vary a lot depending on the rock of which the pea gravel is made. I can easily carry a level bucket of crushed limestone with just a back blade in place on the rear, but 2/3 a bucket or less of igneous stuff with 900 lb on the rear is a little toward the spooky side.
Have you ever seen those roll up tarps for unloading pickups? They cost about $25. Think of heavy duty window shade with a crank on it. You stretch the tarp on the bed, put your load on it, and then wind up the tarp to unload. They're not big enough for the trailer bed, but the idea might be.
Put a heavy tarp or maybe some connected sheets of OSB or something on the bed. Attach chains or similar to the back end. Have some lengths of rope or small diameter dowel across the bed under the boards. Attach the chains to the tractor or a tree, and then pull the trailer out from under load or pull the load off the trailer. That should get most of it off easily.
Of course, you could always have it delivered for a lot less hassle, but that wouldn't be any fun to talk about. /forums/images/graemlins/smirk.gif