1. Dig the shelf. It’s enough to take off the first piece of plywood ( less than 1 inch ) by making 4 holes with a drill at the corners of the rectangle you want to take off, then cut from one hole to the other with a handsaw.
2. Take out the folded paper that fills the inside, it’s easy using the handsaw.
3. Connect by screws the PSU and amp to a wooden board, with some holes on bottom to let cooling air to go around . If you are interested in using more powerful stuffs, then it’s better to use an aluminum sheet, better for cooling and thinner than wood, so the useful space is larger
4. Connect the base and the connector strip using a piece of L aluminum profile
5. Put wires and a LED with a R ( 820 ohm if with 12V PSU )