Wasn't long ago here we were talking about the various roof materials and everyone has different experiences. Personally, I've had aluminum, EPDM/Rubber, and Fiberglass. For me, it's Fiberglass all the way. IMO, much easier to keep clean and not as susceptible to a puncture or rip going under a low branch that drags across the top of the unit. As with all roof materials, it's still incumbent on the owner to keep an eye on it and make sure your seal areas are still good (around vents, the edges, roof appliances, etc).
I've had two Winnebago units...both Journey DP's. Best units I've owned (I've had Newmar and Fleetwood motorized too). When I did significant research on units competing in the same space I was buying in, I'd say that Tiffin and Newmar where the two other top ones to consider.
Both my Journey's were/are just inches shy of 40'. No problems driving and towing a dinghy....you just have to be careful, especially choosing the fuel station you go to. Those stations with fuel isles perpendicular to the storefront where cars are also parking in front, sometimes leave little room to pull into and get out of safely...and with a dinghy, you're not backing up.
The largest gas motorhome I had was a 34' Bounder with the Ford Chassis V10. It was OK, but could bog down on steep hills and wasn't really fun to try to pass slow semi's on two-lane roads. That was kind of like in the movie RV when Robin Williams was passing the big tractor with equipment behind! :-) I personally always thought that the near 40' RV's on a gas chassis was stretching it, but it will work. You may just have to be a little more patient on hills and make sure you have a LOT of visibility and clear lane to pass large vehicles on 2-lane roads.
My two-cents worth.