We have a 2011-ZF25BH11 that we bought new and have it stored inside. Last year I noticed some bubbles on the back wall, this year its both sides of the back wall and right back side. I looked at the roof and wall corners as well as marker lights and they all look to be sealed. Is water still getting in some place or could this be a glue defect. Is it normal for this to show up after 7 years? we use this very little and its never seen snow and stored inside over winter.