Just wanted to add a little epilogue to my winterizing efforts for future visitors.
The low point water drains for my 21MB were located just in front of the trailer tires on the driver's side. Don't know why I didn't see them earlier
. My freshwater tank did not have a winterizing kit but it did have a drain for it. The drain valve is located about 6 inches in front of the water pump connection and is difficult to see and access.
I removed the drain plug from the water heater but it was already empty. I'll be sure to flush it out next spring before reinstalling the plug.
Draining the freshwater tank completely and blowing compressed air through the water lines appeared to clear them out completely so I decided not to run antifreeze through them. My camper does not have a water filter so that was not an issue. I did pour antifreeze in the sink and tub traps and in the toilet bowl.
I've disconnected the 12v battery and 110v power and am calling it done until next spring. Thanks again to all who helped and Happy Camping!