I modify my rat traps with a pop rivet and a square of folded pop can metal.
I never bait the trigger, as the mice love the boxes as well, and if the bait is on the trigger I get more sprung traps.
I have a double mesh wall in the back of my boxes for the bait to go into.
Trap pan is just inside the hole of the box.
My boxes have removeable lids as well which come in handy in freezing conditions when occasionally a weasel/squirrel is frozen in the hole with hips and shoulders on either side. I just swap out lids and carry on.