Update:
2016 - We are now dealing with galvanic corrosion on the entire driver's side of the 770R. Spent $1,000 having an RV place replace the entire driver's side lower aluminum siding. Found NO water leaks, just no barrier between the staples and the al. siding. In the course of 1 year there were holes eaten in the siding where every staple was located. This started in 2015 as small "bubbles". By the next year it was riddled with holes.
RV guy added a barrier to keep the 2 metals apart and resided it on the lower section of the driver's side. Thought we would be good.
2017 - same thing has happened again on the driver's side. It's been under cover the entire time, except for 1 week when we used it. Now has very small "bubbles" again. By next year it will need to be resided.
So now we are trying to figure out if it's got a bad ground somewhere that is accelerating the corrosion - through the vapor barrier that (should) have kept the 2 different metals from touching.