Septic lines?

yes. run hot water and dawn down the lines. There isnt much insulation under one of those. So when you wash stuff down the kitchen drain, like grease or fat and food. It cools down and becomes a solid before before it gets past the freeze point under ground. if the is plugged solid it may be too late to do anything at all. You'll have to call a plumber and have it rooted out. So if it drains slow try the hottest water you can get, if it doesn't drain at all, too bad; make the call.

If the skirting around your trailor is missing or down it will allow the cold air under the home. You need the skirting to trap the heat from the ground and your house. This will keep your sewer line from freezing.

yes if exposed and not buried under ground