The cover in the bottom has a Lid in the front. I rebuild this if yours is broken, or just if you want to build your own or yours is just broken. I added three version. A complete closed one, and one with some circle holes. I buld for me one for a FireFly themed case.

I have a fan in the bottom, so the fan can pull more air out of the case.

I printed mine with the Bambu P1P in PLA-CF with a 0.4 Nozzle and 0.2 layer height.