Thanks for the details. Cooling by the outer shell is an ideal solution, of course!
My current solution (just posted some pictures and description) is neither fully closed nor really “open” to air flow, but I usually get temperatures between 63 and 66. I think that is OK even without a fan. When trying to overclock to the maximum during the hot summer days, the temperatures reached 70 to 75 - probably still usable, but I don’t think I really need that, so I went back to the standard clocking and the lower temperatures below 70.