Just for reference, jer z, Muskrat and Garry, I trapped muskrats under the ice in Wisconsin marshes for 40 years using an unbaited #110 in active runs staked and stabilized with a 4' piece of plaster lath. My #110's shape in this photo ages me somewhat (as do Garry's old Victor Conibears), but illustrates the idea.
Depending upon the lath width, the trap is stabilized at the desired level with different kinds of "wedging" at the spring's eye ring. The trap is positioned just off the bottom in the middle of the run. In predetermined longer runs found with bubbles in the ice to warrant it, I'd set two #110's in that run 4'-5' apart for doubles.
Muskrat, I recall reading about the set types in that graphic in the 1950's - either in FF&G, or in one of E.J. Dailey's or Stanley Hawbaker's booklets, but never tried it. I have no intentions of using them. Interesting that you and Gander Club have found them as a winter trapping tool.
Jer z, Though I have never baited for muskrats in the methods described, I have used bait for them on occasions at the water's edge of ditch banks with half an apple on a stick above the trap. Those who bait #110 triggers use parsnip, carrot, potato or a small piece/slice of cobbed corn with success. Even heard of one trapper who used only orange peels.
Anyway, I was just curious if anybody used this older under ice technique, and you folks answered that question. Thank you.