Here's how I did my flasher strip. Those that will buy the led and acrylic from me will be able to do this when they receive their parts.
First, you need a set of drill bit. Really small to start your hole, than 2 growing from there to 1/4" which is the size of the led mounts, then another one to enlarge from behind so that they properly snap around the acrylic.
First of all, I started with the first and last hole. This way, I'm sure that I will stay aligned when doing the other holes.
Each hole is the same, drill the smallest hole, check your alignment on the panel, then the 2 next, check again. The final hole at 1/4" is done from the top of the panel then flip to the back of the panel.
Use the final and bigger drill bit and slowly, go over your hole just to add a lip around it in the acrylic. This will allow the led mount to clip properly through the strip and make sure it holds in place. Also, If it doesn't clip, you won't be able to insert a 5mm LED inside it. Won't be a problem if you're using 3mm .. and even less if you don't have electronic of course.
Clip your LED mounts through it and install under the panel. Glue with a hot glue gun!! Admire your work!
PS Notice that the lights are not aligned on the strip, you can reproduce that or idealize it by drilling them all centered.