[Topspinmo]

My covers are metal and spring loaded. Most likely moisture getting in when it rains if it only happens during rain. You should be able to see it when you lift the cover of course when it’s tripped. I would also check seal between the cover and the house. Make sure it sealing and not deteriorated leaking behind the cover?

Another thing what even you got plugged in has to be waterproof. If you got extension plug in laying out on the ground where moisture or water can get into the connection it will trip it. You can cover it up or wrap with plastic bag so the water don’t get in.