This is a lone version with just the baseplate I created to store MTG cards in a 20 quart gasket box. 

To use it, print both the left and right sides of the base plate. They are different, so make sure you print one of each. Afterwards, I used epoxy to fix mine together, but you could also go without. 

Here is a link to the gasket boxes on Amazon: https://www.amazon.com/Sterilite-Stackable-Latching-Container-Organize/dp/B002BA5F3O

If you want to see it in action check out my MTG storage system here: 

Props to AnatomicFlack, where I got the idea from a similar insert they created for a different project: