Old work boxes are great. Unless there is an issue with the 2 points the flaps contact on the drywall. This very quick print helps address that very issue. An XL flap for an old work box that provides ~2x the surface bite of the original (original and new pictured below).  This was created out of necessity due to damaged drywall on an existing old work box.   
 

Printing Parameters

• 4x parameters (wall count)
• Support - On
  • Touching build plate only
• 30% infill worked for me, dealer's choice if more or less
• PLA was used, but PETG would be a solid choice for additional strength and flexibility
• 2x required for a single box