The part we will be assembling:
We will be using Loctite Go2 Gel. It works well to adhere the PCB and wood pieces. Flip the pieces horizontally, the smallest piece with the rectangular hole will go at the bottom.
Put dots of Go2 Gel on all visible surfaces of the smallest piece. Lift the medium piece and place it above the smallest piece. Align the lamp holes. This glue does not set fast, so the pieces can be moved to get the alignment right. Once aligned, place something heavy on top for half an hour until the glue hardens. Make sure no glue is coming out of the lamp holes.
Flip the pieces that were glued together and align the lamp holes with the bigger piece. Once happy with the alignment, draw lines on the big piece using the medium piece as a guide. When assembled, this will face down and not be visible.
Now is the time to glue the PCB to the small wood piece. Put glue dots on all visible surfaces of the small piece (not pictured), then set the PCB down on the small piece. Put something heavy over the assembly while the glue hardens.
While the glue is setting, let's get the lamp film ready. Print the film in a piece of paper. First I was considering printing it in clear film, but to avoid driving to the office supply store, ended up printing it in paper then laminating it with clear packing tape on both sides of the paper, then cutting it down to size.
Align the lamp film with the openings. Ensure the letter P is closest to the indexing dot that was drawn earlier.
Using small pieces of Scotch tape, secure the lamp film to the big piece. Use two small pieces on the sides and two pieces on the top and bottom each. Don't use too much tape. Avoid getting tape over the letters. An important thing to remember is that where there is tape, there wont be glue keeping the whole assembly together, so use only a little tape in 6 spots only. The space between the lens film and the pen lines is where the glue will secure the pieces together.
Ensure the LED are in the center of the hole, bend them carefully if not centered. Test the assembly before gluing it together.
Align the dots and be ready to glue the big piece to the other two.
Ensure the whole assembly is aligned.
Then apply Go2 Gel to the space outside the lens film, but inside the lines.
Put everything together and watch the alignment. Put something heavy over the PCB to keep everything together while the glue hardens.
That's it. Put the assembled pieces aside while the rest of the enclosure is assembled.