On 8/31/2017 at 8:36 AM, Chips N Dust said:

That is why in my shop I used those adjustable boxes. They have a screw adjustment so the box can be moved in or out to match whatever thickness you have. A little more expensive, but well worth it to me to have the flexibility.

 

https://www.lowes.com/pd/CARLON-1-Gang-Blue-Plastic-Interior-New-Work-Standard-Adjustable-Wall-Electrical-Box/3497486

Looks like the screw to the left can be turned counter clockwise to advance to box out more.  Per NEC you must have a continuse box.  No air gap  (fire path) but at 1/8" you are still in the gypsm.  I would call your local building inspector as ask him?  Or advance the box out more by turning the screw if that works.

 

 

It doesn't matter and your screws should be long enough anyway.  There is always 1/2" or more sticking out the back side anyway...

  Even those adjustable boxes, another waste of money!