I bought a cheapo travel watercolor pallette from Amazon to do some urban sketching, but half pans are annoyingly small, need refilling too often, and jiggle around too much. I wanted something that maximized the use of interior space in the tin, was more solid than the little clippy insert that comes with it, but could also be easily removed when necessary, so I took some measurements and bashed this out in Tinkercad.

Each well holds at least double the paint that a half pan will. In fact, you can see from the photos that each cavity will actually hold the plastic half pan itself (an accident) if necessary, but I'm not going to use it that way. I like that because of the nature of horizontal lines in the print, it will grip the dry paint better than any plastic or ceramic pan could.

There are 16 wells for 16 paints. Some might say that's too many for urban sketching, but it's perfect for me. Any unused pan could be a water well! If you're the type of person who likes having a huge library of colors, you can print a few of these depending on where you plan to go to paint, like maybe one for nature and one for cityscapes and people. I also plan on sticking some magnets or velcro dots to the bottom of both the pan and the travel case so they are easily mountable to surfaces such as a portable drafting board or travel easel.

In the center, there's a little handle for pulling the tray out with ease. It's just enough clearance for me to grip without putting my fingers in paint, but it doesn't stick out so high that it interferes with closing the tin or dipping pigment. On one end of the handle is a little recess to act as an indicator to tell at a glance which way the tray is oriented (sometimes, your paints are all dirty and you can't tell what's what, amirite?). Put a little dot of your favorite color in there!

The tin used is Meeden brand, but if you look online, you will see that tons of brands are stamped to the same specs, and most are available for 8-12 bucks. I sliced my print in Cura and printed it on my stock Ender 3. It fits nicely to be removed easily with no edge tension, but it fills the void enough to have very little rattle in the tin, quite a bit less rattle than the insert that came with it. If you are worried about fit, print a tester on the very lowest quality and adjust your final print as needed.