What could I use as a metal body for my DIY wind turbine?
Looks to me like a standard 5 gallon plastic bucket, with lid could be cut with a hole for the fan shaft in the bottom and a slot for your mounting pipe on the side. Once mounted, cover the slot w plastic and screw or pop-rivet in place. Wiring will need another hole.
Sun might make the bucket brittle in 5 years, but even with thin metal, you're going to need to do occasional maintenance.