The BGE has porcelain coated steel bands. The Kamado Joe has powder coated cast iron bands.
Below are some comments regarding rust:
Rust
Big Green Egg: Possibly on the daisy wheel and hinge mechanism, nuts and bolts after many years of service. Try to keep your daisy wheel inside while storing it and this will reduce your chances of rusting. Ultimately, there isn’t much that can cause any serious rusting on the BGE.
Kamado Joe: It’s rare, but the nuts and bolts have been known to rust. But again, like the BGE, very little could go wrong with the Kamado Joe.