I'm trying to fab up a 2 piece mounting plate for a lights and siren controller head unit to go into an overhead console. I need the inner piece to attach to the outer piece but won't have access to the back so can't use screws and nuts. The outer one is 2mm thick. Is that thick enough to drill and tap M4 threads for M4 screws? There will be four mounting holes and the head unit I'm mounting weighs under half a pound.