I've seen temps in the 205-210 range, but I haven't pulled my new toy hauler in the high summer heat yet. I bought it last September, and it was in the low 90's when I drove it home. Since then I've only towed when it was in the 70's at the highest.
We're going to the beach a few times this summer and we might make a trip to West Texas. I figure an aux cooler will help keep the temps down, which definitely won't hurt anything. Plus, my truck is almost 8 yrs old, so anything I can do to help the old girl out will be helpful.
2016 Chevy 2500HD Z-71 D/A
2014 Keystone Fuzion 331
DW, 8 yr old daughter, 9 yr old yellow lab