OH Rats,
I totally get not trying to buy equipment if you are doing this for free, consider 2 of the gophinator traps $14.99 for two according to the website, plus shipping of course.
While time may not be money in this case, if you want to be confident you'll get what your after the specificity of the gophinator for a pocket gophers tunnel system is
the way to go.
You can probably buy a macabee trap at your local feed store or hardware, smaller than the gophinator and I personally don't use them but they were the standard years ago
and still are for some folks.
I personally like to situate between two fresh mounds, though you have to read the sign (which with pocket gophers is easier than many species), find the long run between two mounds
that is a longer road of sorts and dig between them until you find that area. While I do set as you mentioned in your description and cover the hole as you mentioned, I get more between
the runs than right below the mounds. I like to think of it as trapping the interstate versus the old dirt country road that you might go down once in a while. The interstate is allowing them
to move across their entire 30' or so range quickly.
I generally set pairs of traps at these locations, one each direction so you don't have to guess which direction they are coming from.
Hope that helps, $15.00 might just save you some head scratchin... (plus the traps of course can be used for a long time to come....)
Justin