So for Iowa weather, wax dirt is probably the best for me, but it’s expensive, heavy and time consuming. But when properly made its almost bullet proof.
Peat moss takes a learning curve, but it can be serviceable, till it rains a couple inches and your dirtholes look like ponds. When that happens the wax dirt is toast as well. You’ve got to buy it a year in advance, and cut the bag open and place it somewhere so it can vent and dry out. A lot of guys use the attic in there garage or the hayloft in a barn.
I’ve found that if you halfway bed the trap around the outsides of your jaws to form a loose imprint, cover with peat moss and pull up on the levers about 1/2”, that will allow just enough peat to filter down under the trap to get it slightly freeze resistant.
Adding a little calcium chloride before bedding will get you closer to the freeze proof range. Then you have to top dress with a little dirt to keep the peat from blowing away.
In regards to the pipedream set, it’s extremely freeze resistant as it is. But if it’s gonna get real cold it needs a little help as well, at least in my soil conditions. I just sprinkle a little calcium chloride under the levers and around the jaws, that seems to help. If you use to much grass it will do a couple of detrimental things, it can crust over if it gets wet, it can clog the jaws, or it will provide sort of a dry lubrication that will allow for a pull out. I use a loose fist size handful and spread it thinly on and 5-6” around the trap to help blend it in. I use only dogless traps in the pipedream set and screens from no bs. Like everyone has said you should be able to see some screen when you’re done.