Refrigerator warms up when driving

Doug, the CU is original and I inspected the drain lines and do not see or feel any cracks or holes in the lines although I think I will replace them anyways soon. I put a plug in the drain line for the trip home and will see if that takes care of the problem. I was not aware that other rv fridges did not drain the same. If this works should I p-trap the drain line or do you have a better idea