I'm building a 12V battery with 4x EVE MB31 cells to be housed inside a Leitner Designs GearPOD on the back of my truck. It's the smaller one on the right in the picture below. Looking for a box that will both fit the cells AND fit inside the GearPOD.

The dimensions in the diagram below are a little misleading. The grooves on the sides and the hinge for the door mean I only have 12.75" from side-to-side and top-to-bottom, plus 9" from back-to-front to work with.

The cells should be 11.28" L x 6.84" D x 8.05" H based on the measurements I've seen (they haven't arrived yet), so they'll fit without a box. However, I'd like to be able to easily remove the battery if necessary, so just strapping the cells down inside the GearPOD doesn't seem like the best approach.
I am having a difficult time finding a box that will both fit the cells + BMS AND fit inside the GearPOD. Everything I've found so far seems to either be at least 1" too long externally or about 1/4" too short internally. Any suggestions?

The dimensions in the diagram below are a little misleading. The grooves on the sides and the hinge for the door mean I only have 12.75" from side-to-side and top-to-bottom, plus 9" from back-to-front to work with.

The cells should be 11.28" L x 6.84" D x 8.05" H based on the measurements I've seen (they haven't arrived yet), so they'll fit without a box. However, I'd like to be able to easily remove the battery if necessary, so just strapping the cells down inside the GearPOD doesn't seem like the best approach.
I am having a difficult time finding a box that will both fit the cells + BMS AND fit inside the GearPOD. Everything I've found so far seems to either be at least 1" too long externally or about 1/4" too short internally. Any suggestions?