I have a 2008 Denali 5th wheel, 31RGBS-M5 and just love it. I've pulled it to Arizona 3 times, about 5000 miles with no problems. I did upgrade tires, wheels and suspension. It has served me well for 4 years now.
I have a 2007 Denali 5th wheel 26RL. It's overall been a good trailer. It pulls well and feels stable. It has 2 slide outs and they have worked flawlessly. It is comfortable and just the right size for us.
Like any RV it's like a house on wheels. They do take a lot of maintenance.
Some of the problems I have had.
The decals started peeling within a couple of years and they would not stand behind it. I'm not sure if they have improved on them since I bought mine. The warranty of almost all trailers are only a year. Pretty much after that the manufacturers warranty is over they wash their hands of their products. So you may want to consider an extended warranty.
I had a circuit panel go out in my furnace about a year ago. Right now I'm dealing with a bad electrical converter and working on fixing that.
Have problems with my brake lights. They use just wire caps on the wire connections and I camp at the beach a lot and corrosion gets in there and messes with the connections.
I would suggest that if you do get a built in generator. It will make your life easier in the long run.
Like I said earlier, it is a house on wheels and things get tossed around when traveling down the road. So it things will happen.
The problems do out weigh the enjoyment the use of the trailer. I believe the problems are overall no out the norm for a travel trailer.