Glen,
Here's a thought: As an alternative to burying and shielding a cable, why not place a passive repeater on your factory roof. Two shrouded yagis, which at LOS frequencies are very small, connected back to back, with each one pointing at the, very small, dish of your tranceiver on its respective side of the factory would work fine. You would have power to spare. Even two repeaters would work.
Another possible LOS solution would be to have a reflector off to one side of the factory, angled so that it relfected signals from each LOS terminal to the other. This is fairly standard procedure for areas where direct line of sight isn't available and the repeater can't be powered. Your shot is so short that you would probably only need a very small reflector, which would have the added advantage of reducing your received signal level to manageable proportions.
Another thought is, if you have to divert the path of the cable around the factory, it may exceed 100 meters in length. Even with shielding, which can,incidentally, act as an antenna and make matters worse, you may find your environment too noisy for easy connection.
I'm all for using cables wherever possible, but coleagues of mine and I have run into so many problems with electrical noise in industrial environments that we are actually developing a bolt on goody which will reduce the effects of such noise in such environments.
Yes it is patented - yes we do intend to make a lot of money!
regards
John