I had it done on my Keystone Outback, but the idea is the same. I had a hitch & trailer shop do mine. They used 2X3" heavy wall steel tubing across and between the frame and between the added cross support and the trailer bumper. My bumper is supported in four places and carries a spare tire and aluminum tool box with a Craftsman air compressor, wooden leveling pads, hoses, power cords, x-chocks and screw jacks. Cost was around $200 and it was money well spent. I had a custom box built that covers half of the rear bumper, fits just under the trailer taillight and sticks out no further than the spare tire.
The long piece on the left of the photo spans across the width of the trailer and the short pieces are what attaches it to the bumper. Without some type of reinforcement, I wouldn't hang anything on these bumpers without beefing it up