Don't put any in your fresh water tank. If you don't get a lot out of your faucets, be sure to pour some into your drains to fill the P-traps with antifreeze, some of it will get to the grey and black tanks from there. The tanks aren't really a problem (assuming you've drained them) because they're relatively large and flat and any ice can expand; but the antifreeze that gets to them from your P-traps will take care of it.
The alternative is to blow out your lines with compressed air. If you do this, you still need to pour AF into the drains.
Hope things are better in mid-April. You don't say where you are, but we woke to this view outside this morning at my in-laws in Wis. Rapids.
1988 Coleman Sequoia - popup (1987-2007)
2012 Roo19 - hybid (2012-2015)
2016 Mini Lite 2503S - tt (2015 - ???)
2011 Traverse LT, 3.6L, FWD
2009 Silverado Ext Cab, 5.3L, 4x4, 3.73
2016 Silverado 2500HD Dbl Cab, 6.0L 4x4, 4.10