This is a slim and configurable case for a Raspberry Pi 3B. It's not a case for systems that runs a heavy load for a long time, but my 3 Pis (pi-hole, openHAB, octoPring) do run with a temperature between 45°C and 55°C measured during summer and autumn (snmp log via openhab). I've uploaded several different configurations, but if you want different configurations you can simply manipulate the attached Fusion 360 file.

During the modelling process I've used this file for test fitting and it matches my three different RPis perfectly: https://grabcad.com/library/raspberry-pi-3-model-b-reference-design-solidworks-cad-raspberry-pi-raspberrypi-rpi-1

Different Model?

Raspberry Pi 3B+: https://www.prusaprinters.org/prints/39044-raspberry-pi-3b-sleeve

Print instructions

Category: Electronics Print Settings

Printer Brand: Prusa

Printer: i3 MK3

Rafts: No

Supports: No

Resolution: 0.2

Infill: doesn't matter

Filament: Das Filamaet PETG Metallic Blau