The Exterior of the RV-walls and roofs...

So we have spent a lot of time thinking about the interior of our future RV but have not thought about the exterior much.  So what does the net have to say about RV exteriors and what we should be looking for?
Exterior Walls
Walls are either wood or aluminum framing. It appears as if wood framing is generally less expensive, more flexible, not a good conductor of outside temperature and relatively simple to repair. However wood walls may rot due to excessive moisture from leaks and wood has the potential for bug infestations.
Aluminum framing, on the other hand, is usually more expensive and more rigid but may require specialized equipment to make any modifications.  However it is not susceptible to rotting but may be susceptible to weak welds from shoddy workmanship. 
So there is no apparent winner here but it is important to know which type of framing the motor home has especially when performing any modifications to the structure.  Also, If you are told it is aluminum framing, then it is important to ask if all sides, roof, and floor are aluminum since there are some companies that state their units are aluminum when in reality they mean the some of the walls or just the roof may be constructed from wood. I have no preference here so we will just note what materials are used.
The Roof
Roofs are made from fiberglass, painted aluminum, rubber or vinyl.  Now after searching the web for the best roofing material I have come to the conclusion that they all suck! They will all either leak or fail over time so again it is important to note what type of roof you have so you will know how to maintain it to extend the life of the roof.
Fiberglass is popular among many but tends to be thin and can crack near the edges but it is very durable. Rubber roofs are cheaper and very durable but tend to chalk and over time they may shrink and crack.  The biggest knock on aluminum is the noise they transfer during rain storms. A more modern membrane roofing material is UV stabilized vinyl, which is a completely different than rubber or EPDM (older rubber roofing material).
Each roof type has it lovers and haters so there is no consensus here either. What you need to watch out for is the joints where the roof meets the rest of the RV especially around the vents and the front and rear cap joints. Those will need to be resealed at some time and visually inspected on a routine basis. Also where the roof meets the side panels is a potential point for leaks so this area may need to be reinforced with sealants. Again there is no consensus as to which roof wins out but there is a consensus that no mater which roof type you have you will eventually have a leak and you will eventually be using a product called Eternabond to patch it.  Eternabond is an expensive "near permanent" solution to rectify  infernally designed roofs. I will avoid EPDM and rubber and will prefer not to have aluminum but the roof type won't be a deal breaker.
So what did I learn about roofs and walls?  I learned to keep my caulk gun, read up on caulks, cleaners and  other sealants and prepare for the inevitable "My roof is leaking..." blog...