Old work electrical boxes

I've added 100 boxes and was done in 2 hours, including primer mudding the box tight with joint compound and fiberglass tape. 
Next day pain touchup..

A 2 x 4 wall rip a 2 x 4 to 2 1/2 inches and the width of the studs 14 1/2 usually. Check after the hole id cut.

Cut the hole for a regular single or double and slip the cut down 2 x 4s into the opening horizontally.

You need to fit the width before the liquid nails.

Put a generous supply of liquid nails on both ends. It may be a bit messy, thats fine. Secure them in place with a few screws through the sheetrock.

They are narrow enough to flip in the hole you cut. The wires will fit behind the cut down 2 X 4s

Secure the box, pull the cable (more than one wire), 

Your ready for mud. Tape, Top, Skim, and texture. Can skip the last two for a smooth finish and sand after a thick Top coat.. You want to finish it all in one day.. Hot mud.. Add a hardener.

You'll be at primer in 2 hours.. You can rough out the electrical and hook up add a cover and flip the breaker. The next day you could touch up the paint. BUT use it in 2 -3 hours..

I installed a dedicated circuit 15 yrs ago with Oyaide R1 outlet, using a remodel box. I’ve had no problem. Then too I don’t unplug my conditioner very much. Just bought a new one and didn’t have any problem plugging it in

Thanks to all who replied. I'm going to try the screw to the side of the stud approach. I think that will give the best stability.

I used metal old work boxes when I ran 3 dedicated lines for my system when I bought my present house in 2002.  I have never had any problems with the drywall caving in or cracking.  I have plugged and unplugged from the lines probably a hundred times in the past 19 years with no problems.  I am using Shunyata receptacle’s. 

Never had a problem with the plastic old work boxes. Get the screws nice and tight and it's done. Keep in mind,  If you use them, you may need to cut the tabs on the receptacle for the plate to fit.