Truck Camper winterizing - Arctic Fox model shown

I watched the video. If it were me; I'd drain out that liquid from the low point drains and not have any liquid in them. That anti-freeze can turn into slush in extreme conditions since it does have water in it as a base(read the msds for the percents).

Also another reason it's good to put antifreeze in the p-traps is so the water doesn't evaporate out and have a direct open air route to the tank(potential smells).