Why not contact Montana and ask them what the recommended upgrade would be? They can probably tell you. As far as tires you will get recommendations for every brand made (it seems) but all will say to stay away from the chinese made tires (good luck). Take all of it with a BIG grain of salt. There isn't a brand of tire made that hasn't had a blowout at one time or another and all get posted. The RVer's that don't have blowouts usually don't post. Keep that in mind.
Asking about tires on here is like kicking a fire ant bed....