The plastic on cheap farm cable like this is not going to be air tight, almost certainly isn't water vapor tight, and probably isn't even 'rust tight', in that

The plastic on cheap farm cable like this is not going to be air tight, almost certainly isn't water vapor tight, and probably isn't even 'rust tight', in that I've seen rust migrate through plastic coated steel fencing and accumulate on the outside. I wouldn't count on it for anything other than making the rust slightly less obvious.