First of all, welcome to MOC!
Some of the full timers will be by shortly to tell you about their experiences with their units in full time paradise—Marsha and I have too many years of teaching left to even contemplate such
—but I would suggest that anything can go wrong on any camper. I have heard horror stories about Montanas on other forums—as well as this one—but about other brands as well. As I am sure will be pointed out by others on the forum, the Montana is the top selling 5er, so when there are more on the road, well, there is a proportionally greater chance for something going awry.
Others will also mention that quality control is an issue in the RV industry as a whole, and I would agree. I know Steve Reigle will respond to this thread and he seems heartened by what he saw at the plant in Goshen that makes Montanas when he recently had his in there for service, so I take that as a positive sign. This is not a bash, but on another forum I heard wonderful comments about the AmeriCamp units and stopped to look at some at a Georgia dealer this week while camping. Looking at the basement construction, I have to say that I feel VERY good about my Montana.
Personally, I have owned three RVs, and had small problems with all. My parents had four and also expereinced small problems. I really believe it is the nature of the beast. Of one thing I can assure you, no matter what brand you purchase, it will demand upkeep. If not, you are inviting problems that might not have surfaced in the first place. I learned that lesson the hard way…