How Cold with a stock 2009 32 QBBS Cat

I have camped down to about High of 40° low of 15° in a keystone outback 21rs. I froze in the cold wind once but not the second time, in the calm 15°. I ran my furnace on high for about 30 minutes to thaw out, when it did freeze. I'm wondering if the cat is about the same, when using water from the tank and using the waste tanks.

Welcome to the forum! It's probably pretty close in performance to your Keystone. To me it seems like the most vulnerable spot maybe the waste valves.

At night shut off and drain the water hose, dump the waste tanks, keep a couple of gallons of water in the water closet to dispose of waste in the toilet, after dumping the waste tanks dump a gallon of anti-freeze down the toilet letting it collect at the black tank gate valve.

Also, get one of those foam cones that they sell at the hardware store for outside fawcets and place it over the fresh water hook-up.
Get yourself a catalytic heater or oil filled electric radiator to supplement the furnace. Hang a couple of 60W bulbs in the basement area.

Make sure that any underbelly exposed piping (at the low point drains) are really well insulated. Also, open the locked 6"X6" hatch high on the side of the curbside of the Cat and insulate the back side of the shower water connections.

I did all this and was quite comfortable down to 4*F.