Reply by Rentvent

I hate working with sheetrock.

You could cut the sheetrock in the adjacent to accommodate the new subpanel. Inside the open square you can drill a hole through each stud on the left and right. Be careful when drilling through the stud that the main panel is on- there might be live wires underneath.

Cut a hole for an outlet in each of the three cavities. (one under main, one under sub, and one in the other side of sub). Be careful cutting sheetrock under main.

Pull all wire and use “old work” boxes.

No sheetrock to patch.

A couple other considerations:
Any 120V outlet in a garage MUST be GFCI or GFCI protected
If using conduit, you can NOT use romex – you have to use THHN wire
120v receptacles should be rated for 20A (see limelight’s picture above – the grey outlets labeled 120V) 20A receptacles cost more and are available in any color.
220V circuits should be dedicated to only one outlet each.
12GA wire is adequate for running 120V or 240V 20A circuits less than 50 feet.