I have a Rockwood Roo 23SS and I would I would like to do something like this:

http://www.modmyrv.com/2009/09/17/rv-custom-bumper-storage-boxes

But in the example above he mounted two seperate boxes. I would like to get one large truck tool box, like this one: http://www.northerntool.com/shop/tools/product_200092924_200092924

My base hitch weight is 458 lbs.

My basic idea is that I want to take some heavy square steel tubing and mount to the steel ibeams that my rear bumper is mounted to. I can mount them so the protrude under my bumper out the rear of my trailer by about 24″. I would use 3-4 large harded steel bolts to mount the steel instead of welding. Then the tool box could rest on the steel tubing and I could use some more hardware to fix the box to the tubes. Depending on the construction of the bottom of the tool box I could run a piece of steel between the two supports to further support the bottom of the box.

Any thoughts before I venture forward???

I would hope to keep the box and the cargo I would store in it under 200lbs.

Thanks!!!