We have the 2010 Montana 3400RL and love it. More than enough cabinet storage and the belly storage is large enough to carry all of my junk. Also the remote that operates all of the slides, jacks, awning etc. is a very nice feature. I did purchase a set of scissors jacks and place in front of the forward axel when set up just to eliminate frame flex/bounce. That accompanied with the SteadyFast stabilizers has made it rock solid. If the 5er that you are looking at does not have the second air in the bedroom I would highly recommend having one installed because these campers are really to large for a single unit in my opinion. The build quality seems to be very good and so far have not had anything go wrong with the exception of the wheel seals giving out and coating the brakes with grease but Dexter made good on that by supplying all new brake assemblies and seals. There is also a Montana Owners Forum that you may want to join and ask all the questions you want. Great group of people and a wealth of information.
HERE is a link to the MOC forum. Good luck and happy travels with whichever 5er you decide to get. Tim