As part of my ongoing effort to create a collection of 3d printed astronomy accessories, I've gone ahead and created a light filter case. It's a simple design that holds 7 filters, modeled to make it easy to grab filters without getting your finger on the glass. The lid is held in place using a set of magnets. The whole assembly is less than an inch thick and 5 inches squared, so it's fairly compact and portable.
The only hardware required is 8 3mmx6mm magnets. The tolerances for the magnet holes are very tight by design, so you may need a rubber mallet to get them seated, once in though - you don't even need glue to hold them in place.
PETG recommended - but PLA will work if you're not worried too much about drop protection
Recommended Print Settings
Outer Walls: 6
Infill 25% gyroid