Assuming that the trailer frame will handle the weight that far back and the extra weight won't negatively affect the way the trailer handles, I would weld a couple of 1/4" plates onto two pieces of seemless receiver hitch tubing (2" ID) so that the assembly can be bolted onto the frame on each side. Then, a 2" square tube assembly can be inserted into the receiver tubes so that it could be easily removed. I would also offset the bumper assembly so that you don't reduce your overhang clearance.
Example of offset bumper tubes.
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Bumper upside down
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