I am sorry to hear of your loss and having to deal with all of this.
This person is an uncommitted buyer. He "thinks" he wants to buy a motorhome, but he can't bring himself to complete the process. Hence the 5 other coaches he has had inspected & all the issues he came up with your delivery. In short a perpetual shopper.
Walk away as there will be some sort of "issue" at the credit union and he wont complete the loan.
I would try to find a dealer that would sell the coach on consignment, you will get less, but you won't have to deal with all the issues that large transactions like this bring.