As stated, dry or wet rot in the cabover is very common in class Cs. All of that unsprung and unsupported cantilevered weight is the biggest reason. Apparently your RV consultant wasn't aware of that. Coachmen makes entry level RVs and you probably got a great deal. The brake lines and repairs would not be visible to anyone without a complete inspection. The rot would have been very visible if someone had attempted to push up on the bottom of the cabover section with their hand. You should be upset with your cheap inspector, not Coachmen or General RV.