If I drain the low points and blow the lines out, there are still water droplets that collects in the sag of the water lines. Whether this is enough to freeze and burst I do not know.
I do know that when I pump in the antifreeze, there is a diluted water antifreeze mixture that comes out of the facets first.
I assume it is the residual water that is in the lines and faucet valves that the air did not blow out.
When we use our TT in the winter we just dry camp and use water jugs for cooking and the washhouse restrooms for the week end.
Also don't forget the "P" traps under the sink need to be drained or antifreeze added after you wash dishes etc.
Our is not a four season TT so a better insulated model may not be such a problem.
Good Luck