I use 3 or 4 double headed nails to hold my bodygripper on a pole set.
find a leaning tree, approximately 3 to 8 inches in diameter, something not full of sticky pitch. If branchy, clear the branches from the upper side to just beyond where the trap will be, about chest high. Drive 2 double headed (concrete forming 16 penny) nails about 2 - 3 inches apart perpendicular to the tree and leave 2 inches or so out. Drive a third nail above or below the 2 nails, centered on the tree, at a little wider space than the gap between the set jaws and protruding the same as the others. The 120, 155, or 160 is et so the lower jaws pinch the nails and are held between the double heads. This is for the triggers on top or off to the side. For a pan activated bodygripper you will use 4 nails, positioned so the trigger will fit between.
I then set the trap on the nails, with the jaws between the double heads, sometimes bending the nails a little for a snug fit. I rotate the springs up, tie the trap off to an adjacent branch, so the caught animal will swing free, out of the reach of shrews or voles.
Wire or nail your bait 8-12 inches beyond the trap (fresh beaver, muskrat, venison scraps) then stick a sick through the spring loops and a few more sticks over the bait and on top of the spring stick lay some evergreen boughs on your sticks for a roof and you are done. You can see from a distance if your trap is snapped because you bough roof will be gone and your marten will be hanging.
It took 5 times longer to write this than it does to make the set. I don't ever use boxes or mailboxes and that is my main method exept for some ground cubbies of brush sometimes.