I Opened my travel trailer early (last week). It is out of state and the temp is to get to a low of 28.?

Do I have to worry? The high will be in the 50's, and it's only one night that it's dipping to 28. I'm sure it will only be below 32 for a few hours. do I have to worry about bursting the lines or the water tank?

I'd keep an eye on it. I'd also do a little research online if I were you about your specific make and model to see what the highest and lowest temperatures are recommended. I wish you luck.