Hadn't thought of two-sided tape. Will consider that. Thanks.

But we are going to need to provide a way out of the pocket for electrical connections for the gauges, so my thought was to drill holes in the back of the pocket for the wiring as well as screws to hold it in place. That way the weight of the gauge(s) would be well controlled and nothing will move.

The whole thing is complicated by the area on the left that slopes very slowly for ~1/2". That means the faceplate has to have a very shallow angle on the left end where it hits that slope in order to be recessed the same as the faceplate for the switch area on the left.

And another complication is the fact that the pocket isn't rectangular. The sides actually hit the back at a slight angle, making the front wider than the back. That was probably done to allow the whole bezel to release from the mold at the factory. But it means that the box won't be a tight fit unless some precise angles are cut on the sides.

But, all that aside I just realized that the same box could the used for switches. So, folks wanting to add switches for driving lights, cooling fans, or whatever could use this box to make things look like the factory did it.