You may not find your answer here, but search the boat forums on towing through the mountains. Prior to buying my enclosed trailer, I wondered why surge brakes were not used that often except on some off makes. Most of my research was around 2010, but it does not sound like things have changed much. Some guys lock out their surge brakes on downhill slopes (using the reverse pin) while others pull over frequently to allow the trailer brakes to cool even if the tow vehicle may be decelerating with only compression. The first option seemed pretty scary to me...