After you blow out your lines...
The plastic lines in an RV are flexible enough to withstand small
amounts of water freezing. The problem is water collected in the faucets/taps will freeze and damage the faucets. When you are done blowing out your lines leave the faucets all the way open to prevent damage from residual moisture freezing. Friend of mine learned this the hard way when found his faucet knobs laying in his sinks after a hard freeze.
The sink and shower drains "p traps" need to be treated with antifreeze. To save a trip to the store you can use the automotive type because you won't be drinking out of the galley/grey tanks.