Can you see if there are any clearance issues with the 24.5 size tires?
I would try and stick with the same size front and back. Match the tire to the weights that are listed and possible go with a higher rated tire. If possible get the coach weighed. Wouldn't go with anything less then 16 ply.
I did a quick search, 24.5 aren't as common as 22.5 tires. Couldn't even find a 275/80R24.5 on the site I looked at.
Here's a 285/75R24.5 I found
When you get prices do comparisons with full price out the door.
I just bought a set of Yokohama's 295/80R22.5 for $3600 out the door. I was disappointed that the date code was 2033, ~10 months old but had limited choices.