My recommendation is still the same. I’ve built a lot of single drives, in fact I build mostly single drives, and have had this problem before.
It’s my opinion that if you put a FOCBOX 1.6 in it it, will perform a lot better. These can be found on the used market.
Adding external airflow (going through the enclosure) with the heatsink would be even better.
Sometimes you don’t even need to expose the heatsink.
This thin piece of aluminum is only thermally connected to the heatsink (on a FOCBOX 1.6) by those two M4 bolts, and yet it actually makes a lot of difference being there versus not being there. And this is a lot easier to waterproof and more robust than exposing the ESC through the enclosure.
This is like “half heatsinked”, not as good as exposing the metal on the ESC case, but not as bad as being bundled up inside the enclosure. It gives the ESC a way to cool off and bleed heat to the outside, through the two steel bolts. It’s also lifted slightly off the enclosure with washers.