waxed dirt is best I've found here to work, been trapping brutal freeze thaw conditions in southeastern Nebraska for 40+ years and I've literally tried everything. Waxed dirt isn't perfect but its closest thing I've tried yet.
I used to be a buckwheat hull guy, but those got expensive and one frost night later you can literally LIFT a solid cookie-like crusted layer off the top of the trap the next check. Salt, calcium chloride, etc. doesn't work at or below zero for me here. In January the ground is frozen rock solid with a frost line that goes down a couple feet. A jackhammer or pick are would make good trap beds and I do use a pick axe seriously for hacking something new out.
I started making waxed dirt in bed of my truck under the tonneau cover and that works on very hottest days of summer. I finally got a $5 old crockpot at a garage sale and it was a game changer. Makes just a gallon at a time but perfectly melts wax at right temp into hot sifted dirt. Its a cheap alternative to cover hulls.
I used to use peat moss too, you have to buy a bale from menards or at
Lowes in very early summer then start drying it out completely until fluffy dry. be patient it takes time and a good dry space to dry out peat moss. Sift out the sticks. It works for a couple days here then it too will take on air and ground moisture and start to freeze up at night too.
A trap in a plastic grocery bag is certainly waterproof but pretty noisy underfoot at coyote sets.
I'm sticking with waxed dirt...only thing I have any confidence in. Controlling moisture is the key, can't freeze if no moisture present. Most dry materials ive used like dry dirt, peat moss, cover hulls, coal shale, etc are like sponges and do take on moisture over time, some just slower than others. You have to prevent that or find yourself doing set maintenance i.e. rebedding traps very frequently. I even tried making sets only in shaded areas. Think shady side of a big round hay bale, or shaded side of weedy ditch, or treeline.. Keep the set always in shade and cold and dry where ground is always frozen vs. Letting sun or warmer areas thaw out during day then refreeze at night. That is a trick that does work a little better but even that will only last maybe an extra day or so more than other more "open" area sets subject to sunlight.
I still stand by waxed dirt and put in a little more wax than you think you need. Make it waterproof.
Buy the wax at hobby lobby and use the free online 40% off coupon. Makes a 10 pound block of unscented pure paraffin about $20 on sale and it will make a lot of gallons of dry sifted waxed dirt. you can buy flake wax in 10 pound bags from trapping supply house but you will also pay shipping on 10 lbs of material and that adds up. Use a block plane and hobby lobby 10 pound block and a plastic tote start shaving your own flakes.
I get dry pulverized dirt from local landscaping business...$10 for a whole loader bucket ull, or about a pickup load for me. Sift out the clods and its a huge supply of dry pulverized dirt. Store it in black plastic cheap garbage cans with lids in a dry place like a garage until ready to wax it.
When waxed store it in sealed smaller containers like clean dry milk jugs or five gallon buckets, like this...you can see them in back of my truck in this pic...
Feel free to PM me.
Jim