I don’t know the coach but I have several comments. You cannot go wrong with a Marathon. They make good coaches and that looks like one of them that has been well cared for. You can detail one until the cows arrive back home, but this one shows that it has had extra care.
It has OTR and that adds value.
But the lack of maintenance information forces you to assume everything needs to be done, or at least very carefully evaluated. I would want to change every drop of every fluid. I would replace all filters, from air to oil to fuel to power steering, etc. on both the coach and generator. I would question fhe age of everything , including air bags, brake chambers, etc and in the absence of information to the contrary would assume they need to be replaced. If you pull an air bag at random and the date code is fairly recent at least you know they are OK.
My gut tells me that is a good coach.