Question about RV trailers?

Well I live in a 34 foot travel trailer and as most of you know the weather has been freezing. The wind chill in Oklahoma has been as low as -10 here. Well, my water line froze up and now my black water tank is froze SOLID. How can i thew this out in order to keep the tank from cracking? And when the temps rise and my tank and water line is free of ice...how do i keep it from freezing again?? The electric box that my trailer is plugged into only has one Elec. out (for the trailer only) and if i plug too many things into the power at the same time, i will trip the breaker. So i can't really use any heat tape until I can find a way to move my trailer to a newer ele. box in the RV park. Which may take a few months.