Thought I would share my neighbor's unfortunate experience with the recent single digits here in Cincinnati. He's not the only one. There were at least five other campers in the park with frozen lines. I had trouble myself but that was because the factory didn't insulate one of the lines on the bottom of my grey wolf. I don't have skirting but with temps as low as 5 and wind chills -10 I don't think it would've made a difference. My problem was fixed easily but looks like my neighbor has some work cut out for him.
From what I can tell his in-line water filter froze and that's where it failed. I know he leaves his tanks open too so his drain line is probably solid. I don't know if he has tank heaters or not. Goes to show even with skirting and heat tape things can go wrong.