Wind would blow away trapped heat--so an engine block in a doghouse is not at the same risk as a tilted OB full of water. Here, boats (OB's, of course) kept on a trailer can have the through-hull for a pump freeze and crack, causing catastrophic consquences when launched, that would not have occured had the boat been sitting in the water. And along those lines, when water temp is 40* and air is 27* then a boat sitting in the water is less likely to have any freeze issues for equipment near the waterline.
Case in point--although I drop my OB on my moored boat when we have steady temps below 25 at night, my neighbor on the creek with the same motor never drops his, and has never had a freeze issue in 10 years.
But my overall point is that the temperature of the air at the weather guage--or even at your porch thermometer--is not the same temp inside the engine block inside the doghouse, when the temps rise and fall 20* during the daily cycle. I may not deal with I/O but I live in similar temperate climate and deal with hoses, equipment, boats, plumbing in an unmanned hunt club, stuff in the garage, etc.