I rarely see 15 amp breakers. I can't remember the last one. in nearly every instance of a gfci popping issue it was water in a plug somewhere, or a bad plug somewhere.
after being reset 20-40 times, then a popping gfci can be more of a load issue.
we try to keep all cord connections out of the gutters, off the ground and hanging in bushes or trees. while I like the idea of the safety caps, I know for a fact my guys will not do it.
I still hate gfci's.