Try to keep all the plumbing inside heated areas.
They built them that way for a reason. I think the old way would let that little bit of water drain from the check valve(in the heat) back out the inlet(in the cold). Then the rest of the water could be protected from freezing by the furnace.
The Drain valves are "low point" Drains Designed to be the lowest points in the system (also need to be protected from freezing). We have two sets one in the front and one in the rear. We have to raise the front of the trailer as high as we can and drain... then drop the front and drain. If they are outside they will freeze and you will not be able to protect the whole system.
Even if you don't PLAN on camping when it is cold. The weather may just catch you off guard. Or tow vehicle failure may have you stuck while waiting on repair. You never know when you might have to do a "Quick Winterize".
I think some others will chime in and give their .02 as well
Have a great day!
TAC # IN 1 Air#27922