Cut a piece of scrap metal so it's large enough to overlap over the edges of the hole you cut in the previous step. (as a rule of thumb: the edges of the scrap metal should extend at least 25mm past each edge of your video control board)

Mount your Video Control Board to the scrap metal, using your choice of nuts+bolts or pop rivets.

Protip: Stick 2 layers of EVA sticky-backed craft foam onto the back of the circuit board prior to riveting the board to the metal. This prevents the board from shorting out against the metal.