Whenever I travel, I often like to bring my ErgoDox keyboard since I have become very dependent on the layout. Ideally the keyboard switches would be protected while the keyboard is in transit. One easy way of doing that is having a cover that sits in between the keyboard halves. It is easy to print such a cover using a 3D printer or cut one with a laser cutter given material of the appropriate thickness.
Since the model is 2D, it is necessary to define the thickness when 3D printing. The thickness must account for the height of the keycaps and how much they extrude from the top of the case. In my particular case, I have DSA keycaps and 15mm was sufficient. I also tried out a thicker 35mm cover that has enough space for SA Row 1 keycaps. You should measure your keycaps to determine the most appropriate thickness for your setup.
Given that I have screws coming out of the top layer through the hex nuts, I included two rubber feet where there is no screw so the cover lies flat on the case's top layer.
The 15mm version costs $56.96 on Shapeways and the 35mm version costs $127.56 (as of writing). It's a good amount cheaper to laser cut (via Ponoko for example) multiple layers of cardboard and assemble them with a few screws and hex nuts. One of Ponoko's P2 sized sheets has enough space for 4 layers. You would spend around $10 total for one sheet and around around $15 additional for shipping.