Did you use the bathroom facilities at all? And you said not the water system at all, right. I'm no expert at all, but I would think that adding fresh antifreeze into the P-traps and commode should suffice. I know others will have better info for you, but if it wasn't used at all, I don't think it would be a problem.
Sorry about the water situation. Many have been in the same situation. Ideally, a tarp is not the best, but it seems like a waste of money to invest in an RV cover for a trailer you may not have for long. Suggest you raise one end slightly high than the other to allow for water run off. Yes, keep the snow cleaned off as best you can....safely. I can't recall what the weight of snow is per 1", but it's considerable. You don't need to make matters worse than they are. When spring comes around and you open up the trailer, be sure to smell for any signs of mold/mildew/mustiness....not healthy and you should probably give some thought to what you want to do at that time. Good luck.
