How to install a electrical outlet box in a workbench?
My suggestion is that you consider installing a ready made plug strip across the back of the work bench. These can be purchased from many suppliers and come with an already attached heavy duty power cord that you can attach to the home outlet. Here is an example of what I am suggesting:



Let me also make another suggestion (coming from an experienced electronics person myself) that you should consider the possibility to install the plug strip up under the upper shelf of your bench instead of at the rear as you have indicated. It is much better for real usage to be able to plug things in without having to reach behind all the junk that accumulates on a work bench.

Here is a picture showing the ideal location for the plug strip. Notice how it is not hidden behind all the equipment on the bench.