How to enclose a buck converter in a battery box?

[batpot]

Was trying to make a 12v battery box on the cheap with a 18650 36v, 12ah battery pack I have.

I got a 20 amp buck converter, and realize this thing is going to get hot....I haven't tested how hot yet, but almost certainly too hot for a plastic box.

Is there anyway to safely enclose this? Or another way to step down?

Trying to avoid disassembling the battery pack.

 

[john61ct]

Need to heatsink it, ideally in the airflow

or it won't even hit half its spec, nor last long