I made a little 10 inch rack mount for my Raspberry Pi 4b (but the 5 should also fit) with a flexiDOCK MB521SP-B

There are options with more disks but i'm not confident it will work (not enough power through a single USB port).

The flexiDOCK is a tight fit and I connected it with a Ugreen USB to SATA connector, you will need some longer m3 screws to mount it as the screws it comes with are way to short.

Why the flexiDock? It looks cool and makes it easier to swap disks if you want to.

I printed it upright/facedown and didn't need any supports

Only downside is the tight placement for the fan if you have a POE adapter. Especially if you use a mod like I did (from https://www.printables.com/model/289387-pi-poe-40mm-fan-hat-adapter). I think I'll print a small half u grill or something to let it vent more.