I ditched the CI grates on my Weber kettle for the same reason. I just could not keep them seasoned.
I tried to pull them off the grill right after my cooks, and hang them inside. That worked, but all it took was for me to let the grate sit on the grill for one night, and rust showed up. If it rained overnight, I was seriously farked.
I finally gave up on them. The costs seriously outweighed the costs.