Bought a used 2003 Montana
Toilet needed replaced after a few months of use the pedal cable snapped
Both grey tanks cracked near the valve area
We still have to reseal the windows.
Roof has some questionable spots near each corner.
The fridge vents don't have seals so they draw in water.
Waste valves are hinting they need replaced
I can tell the sinks will wear out before the rest of the rig.
Awning looks sad when it rains and I've had to poke numerous drain holes. Dunno when I'll get to resealing the layers.
I live in mine full time though so....its WAYYY CHEAPER than a house! If you think of it as a house, it's pretty inexpensive.
Right now the next project is fix each grey tank, add supports so they don't crack again, and add lots of foam insulation to the bottom of the rig.
I think unless you buy a top-of-the-line rig that has a huge bus chassis...you're going to get flex and things wear out. More bracing means more weight and when your minimums for structural integrity on a 5th wheel put you around 14k lbs for a 38' rig. It's difficult to see how they could make it better without cutting weight somewhere.
I can say I think if 5th wheels had less freaking storage units they could save a few hundred lbs and stick that into structural bracing though.... There's probably three cabinets we shouldn't need for full timing, and even less if you just camp.