Speaking of the AC units, Ed, mine have housings that are showing the pain of constant exposure.  I occasionally wipe them with Aerospace 303, but wonder if there's a more permanent preventive coating/paint you'd suggest.  I think they're molded textured fiberglass, so perhaps the same Rustoleum?  
The front one has a crack dead center front working its way straight up from the bottom edge a few inches.  I couldn't get it to close adequately for glueing, so I lexeled it for the time being, just to keep road wind from "flapping" it into a worse condition.  Thought about riveting a strip of aluminum across and under the crack at the cover's edge to draw it back and stabilize it.  I may need to drill a small hole at the leading edge of the crack to halt its spread upward though.
But I think part of the issue is the general deteriorization of the material from exposure.
Joel