There are a few things that you really need to check when changing tire size. One is the diameter. Any change in diameter can affect your speedometer as well as your fuel mileage. If the two tires are within 1/4" it should be no problem.
The second thing is tire spacing between tires with duals. Different tires on different rims have a minimum distance that must be maintained between the tires when mounted. If the tires are too wide/fat, the distance between the set of duals may cause the tires to rub against each other.
A third thing is the load rating. You never want to go to a tire with a load rating below what the manufacturer recommends for your coach. If you go with a higher load rating it may result in a harsher ride.