Elisha Gallup was the editor of the American Bee Journal for some time. Here is a quote from him on what he finds in both manmade hives and trees as far as entrances go and health:
"I had a neighbor who used the common box hive; he had a two inch hole in the top which he left open all winter; the hives setting on top of hemlock stumps without any protection, summer or winter, except something to keep the rain out and snow from beating into the top of the hive. he plastered up tight all around the bottom of the hive for winter. his bees wintered well, and would every season swarm from two to three weeks earlier than mine; scarcely any of them would come out on the snow until the weather was warm enough for them to get back into the hive.
"Since then I have observed that whenever I have found a swarm in the woods where the hollow was below the entrance, the comb was always bright and clean, and the bees were always in the best condition; no dead bees in the bottom of the log; and on the contrary when I have found a tree where the entrance was below the hollow, there was always more or less mouldy comb, dead bees.
“Again if you see a box hive with a crack in it from top to bottom large enough to put your fingers in, the bees are all right in nine cases out of ten. The conclusion I have come to is this, that with upward ventilation without any current of air from the bottom of the hive, your bees will winter well without any cobs.”–Elishia Gallup, The American Bee Journal 1867, Volume 3, Number 8 pg 153
I find most of the feral colonies surviving here are in the walls of houses. All of the houses from the settlement of Nebraska (back in the 1850s) until probably the 1960s or 70s were usually frame houses with no insulation. Bees often move into the walls. Most of these houses still have no insulation. But they do have 1" boards on the outside, building paper, and lath and plaster on the inside. Bees do very well with the heat source of the house. When I find them in trees, they are often very large trees 2’ or more in diameter. Not always, of course, but often. I’m sure they are pretty well insulated by the wood. First you have the live wood with sap then inside that the punky wood which is probably better insulation. It also probably absorbs a lot of moisture.