Custom bumper assembly

I am working on a 1993 26 ft Jamboree on the Ford E350 chassis with a 460. There is very little storage with this model, so I am designing a replacement rear bumper that can secure a 10x16 foot shade canopy, about 3¾ cubic feet of firewood and a steel elevated fireplace made from an old washing machine tub.

In the image below, the red and gold elements are steel angle and tubing. The pink boxes are to be made from pine, as is the blue rack for the fireplace:



Because of the relationship between the spare tire, the trailer hitch and the Yakima bike rack (the green thing), there is very little room to work with. Still, I believe I have arrived at a design that will work, and extends out only a little more than 17 inches from the rear of the RV.

My concern is with the weight. The main bracket alone will weigh some 60lbs, while the firewood cage (the tall red structure) will weigh another 25lbs to 30lbs empty. The shade canopy is one of those heavy-duty set-ups with steel tubing and weighs some 70lbs. So I am looking at 160lbs on the bumper alone, plus the fireplace that hangs off the ladder weighs about 30lbs.

The four bolts that secure the bumper to the frame are big and stout, so I'm not worried about that. My concern has more to do with drivability and other rig capacity issues.

Here's another more up-to-date illustration of the design:



Does anyone one have any suggestions of what else I ought to be concerned with here? Anyone ever done a project like this?