Bait is duck carcasses with lots of feathers pulled and used. The more rotten the duck the better.
I believe the dead ducks bring the tiny critters which is why the ermine is there. They arrive and have hot red meat running around eating the bait. Voles and mice are already inside the box. That is for ermine boxes only.
Marten sets: can't keep the ermine out. Add a Wolverine set, Marten set and a Ermine box at each stop. Otherwise chaos. I know you don't have Wolverine but think about catching all your animals at one spot. Whatever you have, catch a couple of them at each spot. Set lot's of traps. Add a ermine box to each of your stops.
Lure is LOUD. Gusto on a duck wing swinging in the wind. I use Lennon's lures closer to the bait and box.
How to rotten up your duck carcasses before the season:
Remove all meat per regulations. Run 16 gauge wire through the front half and out the back. Wrap 12 inch tag ends in circles. Run wire through the bottom half of the duck the same way. Cut off the head leaving the neck as long as you can. Take off both wings, spread out on board and staple to dry. Later, use the dry wings wired as an attractor with the gusto on the wing. Pull the wings at the end of the season, no lure left behind. Now freeze the one big duck carcass with two wires strung through and coiled up in the back. Put the heads in a ziplock bag with a piece of wire attached and rolled up tag ends. When the big carcass is frozen, cut it in half, leaving the wires frozen into each side of the duck carcass. Now you have one top piece, one bottom piece and one duck head, all wired and ready to go. Now take those bags outside and put them in a garbage can to slowly rot for about 5-6 weeks. Freeze them at their worst smell possible. The trick is to wire the bait and bag it before you rot it down. Keep it frozen while trapping, use an old ice chest for bait. Easier said in Alaska. One duck is 3 pieces of bait and two wings for attractors. Reuse wings each year. I keep them bagged in the trap freezer.
Head and neck piece of bait is used on a running pole, exposed for them to see, not stuck in a box like the carcasses are. Check your regs and good luck. But set 2-3 traps per set.