I own a 13' 2010 Scamp
and here's how I've successfully winterized for the past 4 winters:
First, I make sure the water heater is drained AND bypassed! If not, you can waste ALOT of antifreeze here.
Next, I "blow" my lines out (BE CAREFUL WITH THE AIR PRESSURE! I never go over 40lbs air pressure) then pour 1 gal of RV antifreeze in my water tank (that's been thoroughly drained!). I use my 12v pump to pump it FIRST to the bathroom sink/shower head and commode. This will protect not only those bathroom fixtures but also run into the drain, through the drain pump and hold in the traps. It will also help protect the outside sewage drain valve area. Then I go to the galley sink and repeat.
I give credit to Floyd for this idea, but at the sinks, I open the "hot water" valves, put my finger over the faucet, turn on the cold water valve and it will force antifreeze back up the hot water line into the water heater! Neat trick and it works. I do it in the bath just to make sure the hot water line has been cleared and treated with antifreeze.
Finally, before I'm completely done, I will go outside and press on the "pin" located in the city water fill inlet. This releases the line pressure and in the process will shoot out the water that's in it and usually a small amount of antifreeze will make its way out as well.
This may be overkill for many, but I've never had to replace water system parts that have been damaged by freezing during the winter. I also try to use the "Good to -50 F" antifreeze.
I agree, you can camp with it "winterized", but I personally would NOT go into "freezing" temps below 30 Deg F without my complete winterization process. That's just my opinion.