I have a generac RXSW200A3 transfer switch. The customer wants it mounted inside, recessed in a 2x6 wall finished with sheetrock. It will protrude out a 1/2" from the sheetrock when finished to access cover. Inspector said this is not allowable because it does not have factory knockouts and a flush mount cover. The installation manual states it can be inside, but must be mounted vertically to a rigid structure. Closest I can find in code is 314.20 Flush Mounted installation...shall not be set back more than 1/4" , shall extend to finished surface or extend past. Figured it would come down to manufacturer listing, but nothing out right allows or prohibits it. 2020 code cycle. Thoughts?