When I was setting up two Raspberry Pi as home servers I couldn't find a case to house them together with their respective SSD. So I went ahead and created a modular set that can be extended as required.

The base supports the first Pi with mounts. There are two bodies, one for the Pi 4 and one for the Pi5 which simply click into the base. No clue, no screw.

There are two kinds of separators between the bodies. One is solid and provides mounts for another Pi, the other has a generous ventilation base. 

Both Pi bodies provide space for two 30mm fans. All fans should stick on the four pins provided without glue or screw. (Give them a gentle sanding if you feel too much resistance sticking the fans on). With the ventilation openings there is a very good exchange of warmth. 

The SSD just losely sit in their bays. I provide a body for the external Intenso premium and for the Samsung T7 ssd. These bodies provide the correct openings for the respective cable (see image).

I printed with support for critical regions only and it worked really well. I fixed the Pis which 2 screws 3x10mm (3x6 should do as well). The Pis sit so nicely snug that you shouldn't need more than 2 screws.

The prints you see are all done in Bambu PLA. I use these 30mm fans in the cases.