Should they fix it?

oyarsa wrote:
Bought a trailer in October. Took it out once and stored it with a cover. Never noticed anything happen during the trip or putting the cover on/taking it off.

Today I noticed one of the back rain gutters is almost snapped off. Should I expect that to be fixed under warranty? Should I worry about fixing it if not?

Chances are you "almost snapped off" that rain gutter with the cover. Question is, did you protect the gutter so it wouldn't tear through the cover? My bet is your dealer would say exactly the same thing, so no, owner error damage shouldn't be covered by warranty.