The trailer comes with a water heater. Installing the water lines so they touch the top corner of the air heater is not part of the system. I'm not sure if the top of the heater gets hot enough to melt plastic, but it gets hot enough to touch and learn not to. I discovered it while I was camping. I just stuffed a piece of oak under the water lines that I had with me. The heater doesn't get hot enough to burn wood.
When I got back to town I tied the hoses away from the heater with some zip ties. I guess I could get some longer ones.