During the last week many people have had this problem. I suspect they are like me who covers and stores it out side in the elements. I of course don't know that but it is a good bet. Here in Central Virginia we have had a lot of rain. Nearly 3 inches over the average in June 2.7 to be exact and in July the first week we had about 3 " Exact data was not available but about 12 miles away they had over 3. Our average for July is about 4.5 My smoker has a very good cover and the cord is in conduit fittings.
It does not leak. That I would bet on. The heater element is like a sponge. It will attract moisture from the air. Well how did it get humid air get in it you ask? Well my only explanation is perhaps through the vents. Heck I don't know.
The last time I used it it ran for about 16 hours so I did not think anything bad was wrong. I tried 2 times and it tripped both times. Before I go get a meter II tried the old GFCI receptacle hooked up to a bathroom. It tripped it also. How about one more try on the first GFCI. It may not be a good idea to keep trying the GFCI but if it goes bad so be it. It held and ran at 242 for the next 6.5 hours.
Had It not held I would have connected it to a regular receptacle.
Just food for thought so to speak. When I put the clean racks back in I will make the vents air tight. Jted