Basic 6x3x6 unit Gridfinity tray for holding a large amount (about 100) of #10 size standard envelopes. Cutouts on either end for easily taking out a single envelope. The tabs in the middle on either side help keep the stack compressed while still allowing for envelopes to be removed easily. Has the standard Gridfinity stacking lip.

Even if your bed fits the entire model without cutting, I found that cutting the model down the middle as shown in the photos allowed for quickly reloading the bin with a large stack of envelopes and the added bonus of allowing for a simple, single-switch multi-color print to give it a 3 color traditional post office color scheme!