Attracting Barn owls (any owls) with an owl box seems a bit hit and miss judging by various posts ! I shall definitely wait until I actually see an owl (and/or ask neighbours about their experiences) before going to the "trouble" of putting up a box (maybe on the disused comm's pole near the road).
They have to be around given the amount of protein available, but wish I could just see one.
[Owls were so numerous around my boyhood family home that they used to spook me out with their cacophony of (my) bed-time calls. Those were the days !]