I asked the same thing recently, and was pointed to
ConsumerAffairs.com: Knowledge is Power! Consumer news, reviews, complaints, resources, safety recalls . I think maybe they were beefed up after MY2000. What I found there were two numbers: 75 lb and 150 lb, so I didn't pursue it further, as the box I might have put up there is 210 lb.
Instead, I bought a tiny trailer with a 3'x4'x2' plastic box on it.
I also considered a platform that mounts in the hitch receiver. They're as cheap as $60 at Horbor Fright. It would haul a 200 lb box, but mine is 5' tall, meaning no access to the rear hatch where the spare is accessed and the jack is located.
If you're hauling on the hiway, your greatest hazard might be 18-wheelers in a crosswind, regardless how you haul the load externally.
GB
