I run boinc at 100% so cooling ideas are always helpful. I didn’t see a thread on this topic - did a general search for “cooling”. Here are mine to share - not the best ideas but any critique should be to my benefit. Others can post their ideas or tell me “WTH are you thinking??!!” 🙂

I have two machines that I use.
1. Toshiba satellite (occasionally) - Copper cooling channel was easy to access by cutting out some of the bottom panel. Fixed small aluminum heat sinks over CPU & GPU interface of copper. Of course, now I have to elevate with enough clearance for the fins but I can even get the laptop fan to stop when I blow enough air over the fins with boinc running (at helpful ambient temps, of course 😉 ).

2. Daily driver - https://www.newegg.com/gateway-ne56r34u-everyday-value/p/N82E16834101303
Put this one on a metal box with fan intake port exposed and port grill removed. Removed front panel that covers the memory & drive bays. Finally, I have a desktop case fan (hooked to separate 12 v supply) blowing air into the exhaust vent fins. At night I turn off the external fan since the ambient temperature drops and since the fan is noisy.
When I opened up this machine, it looked like a nightmare to get to the CPU, so I resorted to just cooling the exhaust vent fins.

Feel free to share your ideas on your own setups or mine.