Aluminum bodies should do just fine if they are designed properly. The old Landrovers had aluminum bodies and lasted for years and years. I think it was a bold move on Ford's part and should pay off in the long run. My current tow vehicle is a 2003 F-150 with 235,000 miles on it. When we make the upgrade to the larger trailer we will be looking at a tow vehicle upgrade too. Right now the two front runners are a gently used F-150 or an Expedition EL. I have also been looking at the Ford Transit van as a possibility. Me and the dog like the Expy.
I sold my F350 dually about a month ago, but it was just sitting and costing money. We drove it 2500 miles a year. The turning point was when I went to use it and the inside duals were flat because the valve stems had rotted off.