Good job on using compressed air Al. Good practice as you say. With temps in upper 20's or 30 ish overnight you don't need to be overly concerned as long as the next day temps get above freezing and you are running heat in your 178 at night.
Don't be overly concerned about what the sensor shows as how full your tanks are; they are notoriously incorrect. We go by starting with 1 full FW tank and about 4 gallons in the black tank when taking off. Grey is empty. When the FW tank is near or at empty it is time to drain the other two and start over.
Yes, I use a total of 16 oz. rv antifreeze for winterization. 2 sink traps, 1 shower trap, a skosh for the toilet. I much prefer this to blowing out the irrigation at the golf course. With 4 courses that is a lot of water to move even with a 375 cfm Sullair compresser! And of course it is usually when temps are less than 40, rain and or snow, and lots of wind out of the north. When all went well it was a 6 day test of endurance and patience.
Glad to hear about your heater duct working well, think I will have to copy that. Still biking, yes, very enjoyable here in northern Michigan along Torch Lake, although now it is a bit nippy. Currently using a Specialized Allez road bike, with the 2 water bottles full it weighs close to 20 lbs, that includes a few tools carried in a saddlebag under the seat in case of a flat - also carry a spare tube. Sure is a lot lighter than the tandem we used for many years, a 1993 Trek 200, weighed in at 42 lbs and we both had Brook leather saddles. With 4 full water bottles and tools it was closer to 48 lbs, but then again with two people it was a lot of fun.