J, rubber matting probably is a better idea if you ever plan to make modifications! This most definitely was stamped sheet metal. I did some more research and found out it’s called RC-1. Here’s a nice glamor shot from the manufacturer:

I ended up using the oscillating tool that came with my Ryobi 18V kit. The tool came with adaptor doohickeys for various brands of blades, so I went to HD and got what looked like the sturdiest blade marked “metal”. It worked, but I’m sure a grinder would have been faster. I ended up just taking out the drywall and channel and leaving the fiberboard in place because. (It’s not actually OSB, it’s this really messy mushy stuff.)
The electrical panel cover seems to be designed to actually absorb some slight differences in how far the panel is recessed; there are two metal bits connected with screws and you can vary the distance. I put in longer screws and stabilized the whole business with redwood shims.
Believe it or not, when the inspector came this morning and I showed him my handiwork, he nodded his head and said: “yup, seems a whole lot safer than before.”


I’d been made very nervous by the horror stories I had heard from other people about self-important and/or nitpicking building inspectors. That, and lots of frowny looks on the faces of contractors coming to do bids as they examined various details. Turns out that the building department in this town (a small, low-income suburb) consists pretty much entirely of a mild-mannered and very reasonable guy named Greg who took about 5 minutes to notice that my AC was competently installed and sign the card. I think next time I’ll make him coffee.