Jim has probably hit the nail on the head. My 2006 LBZ has 180k very hard towing miles on it and has never had a problem. I keep the primary fuel tank full at all times through a gravity feed from the 100 gallon aux tank. The full tank will absorb a lot of heat from the returning fuel. Additionally, I always pressure wash the fuel cooler when I wash the truck.
So far so good.
John