In general, every place that a sheet of aluminum is pierced (ie. rivet holes and seams), you have the potential for a leak. More specifically, door, window, and hatch seals will eventually leak and result in rot in those areas. The gasket/drip pan under your AC will as well. In a 70's era (and newer) trailer, the plumbing vent stacks rely on a rubber gasket that has a life of around five years. Also in those trailers, the geometry of the rear end steers water right into the subfloor I'm the rear.
Perhaps less common, but still leaky, are the roof vents, the roof mounted TV antenna, the refrigerator chimney, and the stove vent.