Is this the unit you're looking for Jonathan???

Sorry, but I don't have the dimensions. This box can be made any size the builder wishes. The same construction applys to all sizes.
Use heavy wire or expanded metal on the open-end.
Aprophet... You got it .... THANKS

p.p.p.s. I have one thing to add... To make the trigger more sensitive, on the inside edge of the top, attach a piece of tin to the leading edge, where the vertical trigger/stick hooks onto the inside edge of the box. The drilled hole, where the triggeer goes through the lid, is not very sharp/smooth and the piece of "tin" makes a much better surface for the trigger to hook/unhook to/from when the stick is bumped on the inside.
Maybe that is too much information, but I don't know how else to explain it.
Just put the tin inside before you assemble the box. A couple small finishing nails are all that's needed.