Update...we got home and opened up the lids under the streetside portion of the bed with the furnace turned up to 68.
After a couple of hours we were able to complete the winterizing.
It might be important to note that our 2021 unit is a standard model, with the heater ducts under the curbside portion of the bed. We had some laundry under the streetside portion of the bed, which might have been a mistake.