If it is in good condition and you are within its tow rating, overheating is unlikely, but it can still happen on a very steep grade on a very hot day. If the gauge creeps upward, slow down until it settles. Otherwise, stop and let the engine cool for half an hour. Also remember that when doing downhill with a load hitched behind you, it is best to stay in a lower gear at a slow speed, and never riding on the brakes - this can also lead to overheating, among other potential disasters, should you lose control of the trailer.