Just purchased 2012 Sierra 2500hd and after a car wash the paint around rear fenders had water bubbles under the paint to make a long story short the body man who is installing new wheel arch panels said this is a thing with all the truck manufacturers Ford included. Because of government mandates on auto builder's to reduce emission on the total fleet .One of the ways to do this is buy thinner body parts to lighten everything plus the truck looks good and cost less to build bigger profit. Body man said because of the thin steel they have gone to spray foam as a stiffener and sound deader. These 50 to 80 thousand dollar trucks don't last any longer the the trucks back in the 70's that cost about a 1/4 of the trucks today. Almost all the rust proofing shop have been closed but they are on the come back because of these over priced rot boxes. The new chevys have already got complaints of air getting under paint at a stone chip causing the paint to lift off. Not sure what Ford has done to prevent corrosion but I'm pretty sure salt will eat them also.