A roll of heavy ish 3 strand household wire works good for getting chains through tough spaces. Straighten it out, push it through and twist a loop to attach a chain hook and drag the chain back. Coil it back up and toss it under the bunk till next time.
Well you should learn something everyday, and you just taught me something. Not even sure when I would use that, but it would be worth tossing a piece under the bunk just for that.