Nothing really new here but this is how I am applying some of what I have learned from others on this board and elsewhere:
I think using top entrances has a lot to recommend it. There is, however, also the need for an entrance reducer for top entrances up here due to blowing snow in the winter. Nearly anything will do, even stuffing in straw in the fall but because we like things to look a little nicer and there is some benefit of standardization I have worked out a system for top entrances by modifying commercial equipment.
First I take a standard migratory cover and glue a shim to either side to make the entrance. I also drill out the edges to receive bolts which will hold the entrance reducer. I keep a piece of drilled out trim (see below) handy when I set the bolts the proper depth so they will hold a reducer snugly. I then apply a small amount of glue to help keep the bolts in place.
The entrance reducer is made by cutting a piece of trim to length and making 3, 5/8" holes with your standard drill. One to receive each bolt and third for an entrance. The entrance is off to the side so that any snow that might blow in stays off of the center of the hive where the cluster is most likely to be.
This ought to
work as well as standardized equipment in keeping bees alive through the winter. I guess I would need a ten year double blind study to say for sure. Or perhaps you see a problem and can save me some heartache?