I have mine on an upturned plastic garbage can about 3′ off the ground near where they sit before flying to my feeder. I have a piece of plywood under the trap. I started with the trap on the ground, but I was catching a lot of juncos and a few wrens. Then I went to some concrete blocks, but was still catching juncos. When I got it up on the garbage can, I’ve only caught HOSPs. I’ve thought about getting a post to mount it on.
I use a pellet gun to dispatch them, and it is quick and humane. I use a wheelbarrow to move the trap into my garage overnight, where the temperatures stay about 20 degrees above outside. So far this winter, that has worked well. I try to keep two decoys, as they seem to roost together at night for warmth.
I’ve caught 41 in the past 5 days… 209 since mid-summer, when I got the trap. But I have at least that many in a pyramidal arborvitae hedge in my back yard. I got the trap to reduce the HOSP population in that area. In the winter, the ground under that hedge turns white(and not from snow!). 
The hedge screens my garage and, in the summer, my RV, so I don’t want to remove it.
Since I’m home more in the winter, I have the trap out constantly now, as in the summer, I was always going to one place or another.
Some day I’d like to try a bluebird house, but that’s just not possible right now. But, my cooper hawks and raccoons are eating well! 
Chris
Toledo, Ohio