Big stuff can be done in Evapo-rust, too. You'll need a plastic trash bag of sufficient size. Put a bunch of sand, or something similar into the bag, lay it flat and then press the item into the surface of the bag, displacing the sand, and making a part shaped depression into which you put the part and Evapo-rust to cover it.

Evapo-Rust can be used over and over, and it's not nasty.