The silicone oil thing is a neat idea. I've seen a few car audio installs where a naked amp is suspended in a fish tank filled with that oil and it runs fine (and cool).
For that small of an area filled with oil, I still would find a way to mount a heatsink to the outside of the box, but in direct contact with the oil, so the heat has somewhere to go.
I test run this for some time, if all goes as plan, i do get bigger box, so i can make better inlets, place for heatsink (if there is need for that).
My first plan was to use MMM, but Joe from CC did say that my beta testing voids warranty ( ), so i did use my old MM what is worked reliable looooong time.