I know absolutely NOTHING about Fisher or Marten. But correct me if I am off base, in winter don't they both eat squirrels, chipmunks, mice and occasionally rabbits, a bird or two? Never heard of them eating mast (nut) crops. Wouldn't whatever they are feeding on that time of year be most attractive? Beaver and venison might be overlooked in a cubby but a squirrel skin or chipmunk might entice one better than big game parts. Here, if you want a mink to enter a mail tube it better have some feathers/fur hiding whatever bait you choose 'cause he will take a look with that long neck and if exposed at all in that "cubby", his curiosity for the bait is satisfied. He is less interested and maybe on his way. Like i stated "I know nothing about those fishers but here I hide bait in a cubby with fur or feathers to get an entrance response. My experience with a different animal type. .............the mike
You are right about fishers eating small animals especially in winter. Here in PA if you open to see stomach contents, you always see squirrel & rodent hairs. Fishers are tough on squirrels in my part of state. But for bait/lure in winter it's always a good idea to use a loud lure like skunk to attract animals. As BruceT said beaver is a great bait, especially with salt added to keep it louder. The fisher do seem to run the streams here, just like you were trapping for coon