I'm building a speaker cabinet out of a bee box I bought. The bee box has handles carved out of them that I need to fill flat. It will then be wrapped with tweed so what the filled part looks like doesn't matter, The main thing is it can never rattle it it will sound terrible in the cabinet (that will have a lot of vibration) and it needs to be flush or sanded flush once filled. Was thinking I could chisel our square and glue a board in it. Or if it's just as good and easier fill it with something like bondo or liquid nails or something. But don't want it to vibrate loose in 5 yrs. pict if what I'm talking about below. Thoughts?