Howdy and welcome.
Usually, separation at the seams indicates structural problems - specifically in your case, rotten wood inside.
The aluminum corner molding is usually attached to wood framing inside the trailer by screws. When the wood rots, the screws have nothing to hold them in place, so the molding goes wherever it wants to.
The proper fix for that situation is to remove the molding and carefully peel back the siding enough to determine the extent of the damage and replace all the rotten wood - then reassemble it all and seal it up properly.