Well like I said mine is a 12 so dont know about any changes to the newer ones. but here it goes:
1. Fiberglass roof on mine guess same for newer.
2. Ride is subjective, we have those flex-frame seats up front, I would rather have had some adjustable seats instead. Elec adjustable is what I would have preferred. The ability to turn them around is not a big deal. Driver seat is a PIA to twist around, passenger seat is ok but the seat sits about 4 inches lower than the coach floor! So not much good IMO for anything. Ours we leave as is.
Mileage is typical for the class about 8 and if lucky sometimes 10 (nebraska with tail wind). I also installed a 5 Star tuner to make the engine more manageable and the trans to shift better. You will need to figure out if stock is to your taste. We run the air suspension at 55lbs or so. less the thing wallows, may install a better sway bar system but the air bags with more air helped a bunch. ours weighs in pretrip at almost 13000 but we dont carry much may 1/3 tank water full lpg, dump the waste tanks often. just me and wife and so not much stuff in vehicle. I did get one of the 100 psi hotdog airtanks for tires. rig also has aluminum alcoas and they are PIA to reach inner, so if you can get extended valve stems installed. I run the long extenders sold at camp world.
3. It should be rated for 5000lbs and yess you will know the towed is back there. Our hyundai is around 2800-3000, tows well but yes in hills you will feel it. In colorado around denver runs out of power so you are in right lane around 40mph. also will drop if you go up wolf creek to about 40-45 if lucky may go lower. actually wish it had the diesel engine in it.
if can be any other help just PM and we have at it.
Yes fiberglass is better. as to speed we stay at around 65, get same mileage even if going slower.