I did the same thing with my Templeboards and wired in a USB jack, an XLR jack for the FC-12, and 1/4" In and Out for guitar and amp outputs. Super clean!
+1 for Zenrigs, I use them to mount my FC12, Mission Pedal and EV-1 to my Temple Audio Board.I used @ZenRigs Man's mounting plates along with Temple's native mounting system and extras of the dual-sided tape squares to mount my two FC6es. Should work perfectly for the FM3 also.
Solid as a rock with four of their medium pedal mounts spaced out near the corners, and no worries of issues with too-long screws poking holes in PC boards inside....
M3.5 16mm works, i hard mounted the EV1 as well.
Appreciate it gents!M3.5 screws of 16mm. Take out original screws, use the new ones (perhaps with a washer).
Can't check if it works, as I have not yet received my Fm3 or templeboard (but I do already have the screws ) , but this is what people say works perfectly.
Alternatively, use a small piece of wood to attach it to the templeboard, and then on the wood and Fm3 use velcro. Be sure to not block the vent on the bottom!