I'm making a few weasel boxes. I see some people make a hole in the back and cover it with hardware cloth to help let bait scent out. Good idea or not? We can get quite a bit of snow here and thinking snow could fill in from the back.

That powder we get could be a problem maybe skip the screen and smear the lip of the front hole instead.

yes just do it
the hardware cloth is perfect

Hardware cloth or holes drilled in back are both ok.

I like an overhang of about 3-4 inches on front of boxes. Helps when it snows. It keeps entrance hole visible

Instead of hardware cloth I just drill a bunch of holes in the back side of the box. Just less work.

I just smear some scent on top,

Just cut the back 1/4" shorter than the sides.

Keep your weasel boxes simple, use a milk carton stapled to the trap with a pan trigger:

I made a few of the fence slat weasel boxes, they seem to work fine...

Weasel boxes can also be made longer to hold a trap at both ends.
Any body who goes after them a lot ever try that? Worth the extra time?