I use "grip nut", glue with epoxy inside the fuselage when it's possible, when you built your plane.
Otherwise for ma Bearcat ESM, I use this type of nut, for wall mounting. Not so light weight, but it's forward, so.. Less weight to put in the noze to balance the plane!
And this "nut molly type" is very interessting because you can install it without dismantle anything if you have cowl fitting problem.
