Finally got a couple of hours to devote to the humidor project. I used a nibbler to rough-cut the hole, and the tip-ends of right-hand tin snips turned upside down to make the left-hand cutters. The snips can hold a fine line. If you cut on the outer edge of the black mark made using the template, and then there's not alot of filing to finish-of the edge. It's a 2-1/8" diameter hole that lets the gauge drop in easily. Put the cardboard seal back into the lid, trace a hole using the edge of the hole that's been cut. The cardboard seal is brittle. Cut it with a new blade, on top of another piece of cardboard so the blade can sink in.
Cut-off the tip-end of the sealant tube so the discharge hole remains small. A single bead will do the job and then wipe the overage off with a towel dipped in acetone. Acetone will dissolve the sealant, so stay away from the gauge bezel.
The battery tray can still be accessed.
The gauge took an hour to normalize up to 62%. Then, last pic, I opened the jar to atmosphere and the humidity needle shot up to 64%.
Fantastic cookie-jar humidor.
Thanks LN420 for a great addition to better living
.