I have two cast iron accessories, the swing grate and a heavy CI grate. Both rust badly. I store them in the garage, which while not climate controlled is completely out of the elements.
I've tried re-seasoning each on multiple occasions, something that worked great on a rusty DTMF that I purchased used.
I live in Austin, TX where there is some humidity but not super high levels.
LBGE & SBGE. Central Texas.