I got on the scales and my 2005 F350 CC DRW with 9' steel flatbed and toolboxes weighed 10,500. I've been looking at an aluminum flatbed myself.
You can probably find an aluminum dump with a steel underbody that might hold up. Not sure, though. Wouldn't dump a lot of big rocks but then again I wouldn't do that to steel anyway.
Are you trying to stay under CDL?
"You Can All Go to Hell, I'm Going to Texas." --Davy Crockett