Sorry to dig up an old thread here, but I've just discovered similar rot to the rear cross member on my F350. Found it after hearing my spare bouce around. After reading some of these responses I'm most likely going to have a welder take a look at it as I'm in the New England and haven't found anything at local salvage yards. Do need a gut check here though....until it's fixed am I pushing my luck doing any local (non-highway) towing? It's a class V receiver bolted to the frame. The frame in the area of the receiver bolt up has surface rust, but is pretty much solid. Average load of the trailers I'm towing is about 2000K with 250lbs tounge weight.