anyone ever install a fan rated box in a SIP lid? i tried to talk the gc into building some kind of decorative block, securely fastened,to the osb cieling and then just drywalling around that. he didn't like that idea, so i cut a 3 5/8" hole, dug out a bunch of styro, and hammered a 12" 2x4 into it. then i secured a F/R pancake, shimmed out to match drywall, onto the centered 2x4. is there a F/R box out there that would be a better match for this application?