Here is my pen storage system I am working on. I am up-cycling empty gravy containers to make my pen storage. The storage unit will continue to be added to as we finish more containers. I started off with two gravy containers. They are made of very thick cardboard which makes them ideal. Some have cardboard bottoms and some have metal. I have used both kinds, but prefer the cardboard.
I painted them white with some cheap acrylic paint. It took two coats. You could use whatever paint you liked or even decoupage them with your favourite paper.
I then held them together with an elastic band as the paint was still slightly wet they are now stuck together. I then added a third one and will keep building on this as I finish more gravy pots. They are ideal for all your pens particularly your dual ended pens as they lie horizontal when completed. You can find different sizes of gravy pots to make compartments big enough for all your pens. If you have a big collection of a type of pen you may want a compartment for each colour family. At the moment I have my promarkers in a different storage system but may convert them to this as the unit grows. Presently I have all sorts of different pens in this system, including gel pens, crayola pens, peel off pens and fineliners.