What about just a deep metal box with plaster ears like a 3x2x 3-1/2" deep and either using holdits (battleships) or screws through the ears into the wall?
Steel City 820-D good for 2 3/4 '' thats all I use. Just cut them down. This way I only stock 1 size in truck. I would use 3 1/2" metal old work box, with the clamps in it. depends on M/C or Rx. If it is double rock it may be fire rated?