Understood, however I remain suspicious. My logic is that towing causes the brakes to run just a little hotter, aggravating an issue that doesn't surface till the brakes are abnormally hot.
If you suspect ABS or another electrical/electronic problem, can you disconnect your trailer brakes (pull fuse or circuit breaker to the controller) and still drive safely enough to see if the problem goes away?
A weak ground can scare up all kinds of demons. Is all the wiring clean and tight?
***Please*** let us know what it turns out to be.