No matter which type of exterior siding, I recommend the Lucas Oil spray wax. It is easy to apply and buffs quickly and easily to a nice shine. But even better, it makes it easy to clean black streaks and bugs. I apply a coat to the front cap before every trip and the bugs wipe away with a damp cloth. It's what the hot-rodders use at car shows. (Ever wonder how they can drive 200 miles to an event and the car looks spotless?!)
I had fiberglass on my Outback. Had delamination bubbles on the upper front cap after about five years - no water intrusion - just heat and the fact the panel was flexed so much. Also - the side that faced the sun in storage lost its shine after about five years, from oxidation. I just got my aluminum sided Jayco and have yet to form an opinion. So far, the black streaks wipe away more easily than on the fiberglass.
2015 Jay Flight 32RLDS Elite
2012 Chevy 2500HD Crew Cab LTZ (6.6L Duramax/Allison)
Equalizer Hitch (1200# bars)