I pulled the bottom panels off the MFC and expression pedals and used them as templates to drill holes in the panel they're all mounted on to match the devices the bottoms mated to. Went to the local hardware and got replacement screws that matched the original bottom attachment screws but were 1/4" longer. Left the bottoms off everything, and just screwed through the mounting panel into the devices. Those things are going
nowhere.
The two Boss FS-6 pedals don't have bottom panels, but they're pretty lightweight so I simply mounted with velcro. Hate it. Every time I move the thing, the footswitches separate from the board. Supposed to be "industrial strength" velcro, but I don't know what industry they tested it in. I have to be able to remove those anyway, since they require batteries, so I think for my next trick I'm gong to get some snaps and rivet one side to the mounting board and the other to some leather strips and strap 'em down that way.