I ran into some Berkley Steelon Nylon Coated wire in 20lb strength and am wondering if anyone is using this material for construction of intruder type trailing hook flies?
Yes, and my advice to you is - Don't do it.
Braided wire has a tendency to kink when looped around the shank of an octopus hook. If you are only planning on catching one, maybe two fish with your fly, then by all means use #20 wire. After a couple of fish (or a couple of hangups), the wire will break where it loops around the trailer hook shank. Even small fish, even light hangups, even accidentally whacking your fly on the rocks during a cast - all will stress the wire, and the wire will break, sooner than later.
I found this out several years ago after buying a spool of #20 steelon and proceeding to tie a couple hundred client flies. To my horror, every single fly I tied with that trailer material had some sort of wire failure after only a few fish (some after only a few bad casts), and on all of them the wire broke or frayed in the exact same spot - where the loop of wire goes around the shaft of the trailer hook (octopus style).
I have since moved on to 25#-40# mono, depending on hook size. I used to use fireline, but the coating frays after awhile and as the now-uncoated fiber frays, the floppiness will cause a fella to miss fish as well as lose hooks off the trailer loop by it slipping thru the eye gap.