I built a prototype yesterday. Thought I'd share my design and see what people thought. Think of it as a shallow super full of insulation, metal on top, and a 3/16th bee space on the bottom like an inner cover.
I believe in insulation on top in the winter. When a colony is trying to control the temperature inside the hive it seems insulation would make this job easier (In the summer and the winter). Feel free to discuss that if you want but I'd rather talk about the upper entrance...
The idea is a tunnel making it easy for bees to control the air flow in and out, but air would not move on it's own.
This entrance goes straight up then back down and out of the hive, meaning warm air shouldn't simply rise up and out without the bees' help.
I'm still trying to figure out if simply putting a rock on top is sufficient or if I should find some other mechanism for holding it down.