All some interesting perspectives. Let me try to view it another way taking the OP Coach & a RV out of the equation.
A person buys a $400k vacation house. Has it for a full year plus and has no issues. after the warranty expired, he / she noticed a problem with a water leak coming in from chimney. They checked out the seals and couldn't find any problem, but to be sure they had two local roof service people come in and double check. They couldn't find any major problem either, but put sealant around any possible points.
Point A: Given it was a known leak, and NOT found by two roofers; what does it say about the roofers? If it were my vacation house and they could not find the leak; I go back to the homebuilder.
Point B: Knowing root cause was never found, seems like every time it rained in the area of my vacation home; I go back to see if it is leaking around chimney or not; just to see if sealant had any effect or not.
Point C: Given for personal reasons you were unable to get back out to the vacation home for 6 months, why not have one of the 2 roofing companies go out & follow-up on their repairs?
As a result of sequence of events you would later learn that the wood from the roof, 2nd floor, and 1st floor of vacation home is wet rotted and with mold.
So now we call in an authorize agent of homebuilder to get their opinion. They say they have to take out the chimney, with an estimate for $17,000. You agree to pay, but then they realize that support beams are also wet rotted and needs work and it is going to cost a whole lot more!
So what do we do now?
A) Bash the Homebuilder who at this point has no earthly clue as to what is going on?
B) Question or doubt the Authorized Dealer because the
damage is more than what was expected?
C) Sell the Vacation home, because of large negative repair investment?
What about holding some accountability? Problem was properly identified by owner. Leak was not detected, nor fixed by two repair entities. If your homeowners coverage did provide coverage for this repair you would have to be careful in telling them the whole story, because Insurance company may say the owner did not take proper preventative action with a known leak. If insurance did payout, I am 100% certain they would find ZERO liability with homebuilder.
So if it were me, I would conclude, the Homebuilder may be my friend. They may best be able to fix the issue with your vacation home today. I would never call or use the two repair entities again; as if they have their fair share of negligence (incompetence). Point could be made that if Homebuilder had had a chance to rectify the problem, and could NOT find anything; and this happened, some liability could persist. But I doubt the Homebuilder would have just put sealant down when they didn't know where the leak was to fix.