I like the fiberglass exteriors, too. They are more dent resistant than aluminum and they look nice to my eye.
About water intrusion problems, these can happen with equal ease in either type. We had a post on this forum just a few days ago from someone who bought a used Aerolite and then discovered problems. Aerolite was one of the earliest to adopt aluminum stud framing that held a fiberglass-foam-lauan laminated sandwich construction. But this new owner found that the trailer's roof had been leaking and the foam was so saturated, when he started to mess with the ceiling the entire thing was coming down. The foam used by most of the RV industry does not resist water. So any time a roof leak goes undetected, there's potential for mold and damage. Doesn't matter if there is wood to rot or not.
The only type of trailer I've found that isn't subject to wall and ceiling degradation from water intrusion is the molded-fiberglass trailer. The best of these is probably the Oliver, sold factory direct in TN. Even so, one still must be vigilant for water line leaks, window leaks, doorway leaks, vent seal leaks, etc.
