Put each lid into place. Press it down and fix in couple of spots with solder. Then solder it continuously around all sides.
The rail in the picture has the small parts and the big part in wrong order. Solder it with the big one over the small ones.
Clean the rosin flux from ouside using isopropyl alcohol and the toothbrush. Pour out the liquid that got in through a corner and dry out.
Print the 2 labels. Glue the big one on the top of the box so that the three longs strips "POWER SIGNAL SIGNAL" are on the side with the connectors. Glue the small one on the short side of the box which has no cable.