In our prior RV we did the full AF routine, but with our current rig we blow out the lines and just add AF to the traps. It is certainly more risky just blowing out the lines, but done properly it yields the same results.
One winter I went out to the rig (stored in backyard) during a severe cold spell where wind chill was nearly 30 below and found the half full bottle of AF I used for the traps nearly frozen solid. I thought worse case scenario it would get slushy, maybe it was a bad batch although I had just recently purchased it from Wally World.
Be very cautious if planning to just blowout your water lines unless you know the layout of your rig's plumbing system, one misstep could lead to catastrophe.
