Turn your electric tank heaters on and leave them on in cold weather as they are thermostatically controlled . As for the hose. ALWAYS disconnect the hose from city water when camping in below freezing weather. Hopefully, you didn't break any water pipes in your RV as even with the enclosed underside, these units are designed for "cool" weather or short periods of freezing weather, not extended periods of COLD weather. In my opinion, you'll be fortunate to not have broken water pipes under your RV! Best of luck as things thaw out, my experience would suggest you'll need it.
Days camping (2015)----88 days
Days camping (2016) ---110 days
2016 Wildcat MAXX 28RKX (33' TT), 2007 13' Scamp
2015 Ram Laramie Hemi
30 years RV'ing
12 different RV's