I recently got this baseball display case from amazon, and I really wanted a frame for the bottom to make it look more “official” so I went ahead and designed a simple one myself. The dimensions of the cutout of the case are 82mm x 82mm and it has a depth of 7mm. So if you have a case thats bigger or smaller than this I'm sure you can do the math and adjust the scaling to your needs. I made the hex cutouts on the bottom to save a little bit of filament!

I also added the test file I used if you want to use it for your scaling or if you want to use the frame as is! I initially printed the test file to make sure it would fit just right around the display case, then I printed the entire thing so I didn't waste a lot of filament. If you have the exact same display case you don't need to print the test.

I printed at .2 layer height, and 15% infill with matte black PLA.

This is the case that I purchased in case you have been looking for one and want to use the frame I made. 

I'm still learning how to CAD, otherwise I would have made it a little fancier, but I also like the simple look it has right now. If you print the model post a make, I'd love to see em! Wreck 'Em!