I have my M1 mounted in a 19" rack system,I,m working in that now,move all the components from a 14"in wall box enclosure and mounted in a rack syst I custom made from a aluminum piece,also I mount some M1 modules and all my leviton stuff,I dont include pictures because I think you don want to see an unfinished rack.
excuse me my poor redaction!
The obvious drawback to the metal canless mounting method is less security for the burglar alarm system. ie. easier for a burglar to get to the security system and disable it, but in my case it is hidden and locked away in a protected closet.
When you do any of this DIY mounting, the UL listing is no longer valid.