1) Not in my experience, factors other than length matter more, and MPG is determined more by frontal area and how you drive.
2) Some B+ designs are lower and narrower than most C's, and some cap designs help slightly with drag coefficient, so on the whole, B+ is better MPG, but that depends also on which specific model, whether C or B+.
3) I know you can get either a locker or limited slip for the axle used on the E-350, Ford offers it as an option, and limited slip shows up on some emergency vehicles, but RV manufacturers don't buy the option. If what you really want is a locker (drag racing or rock climbing?) you must buy aftermarket. Don't know about Chevy, whether using Dana or GM on the cutaways.
4) Whether or not E-350 is sufficient depends more on weight than length. A 28 with no slides could be a lot lighter than a 22 with two slideouts. E-350 offers opportunity to get a V-8 that does better with MPG, which seems to be an issue for you, or if you find the right one used, a Powerstroke.
5) Your local Ford TRUCK dealer should have an excellent brochure on the E-series. I've been collecting them since 2005 and find them more useful than Ford's website, which doesn't have all the information in one place, you have to make multiple "build" passes to draw out answers. I've not found a comparable brochure from Chevy, but my local dealer may not really be a truck dealer.
6) I don't think you need a power leveling system on anything, but the larger the RV the more work it can be to level, and yes the systems are nice if your leveling problem is in the range of operation. C's do not usually have power leveling, the cost works against sales in the price sensitive C market. If you are thinking off road or back road, power leveling tends to add to a motorhome's already difficult clearance problems.
7) Whether a C (or A, or truck camper, or van) handles well or poorly depends less on manufacturer, more on whether the house is too big for the chassis, and the distribution of mass and surface area relative to pivot points. It also depends on who is driving it, expectations, experience, and driving skills. I know that driving a 22 foot (overall) box truck on Express 3500, E-350, E-450 cab-chassis, especially lightly loaded (about 8000 GVW), feels like a sports car compared to my 12,500 pound 30-foot motorhome on the same chassis. But what a 22 footer filled to 12,000 to 14,000 pound capacity feels like, I don't know, because I haven't rented a box truck to carry a heavy load, only lightweight bulky loads.
๐ Mass producers Winnebago, Thor, Coachmen, Forest River, Fleetwood, Jayco, use similar construction techniques, a box constructed of laminated panels stiffened by aluminum frame members. There are differences on how the box is assembled, Winnebago using interlocking aluminum members, most others using point fasteners. Forest River and Winnebago have been skinning the roof with fiberglass sheeting, others are still using lighter synthetic fabrics. If you inspect different mass production RVs closely, you will find significant differences in fit and finish, materials, type and number of fasteners, quality of other hardware items.
Holiday Rambler built motorhomes differently, with aluminum framing built up from floor, then skinned and filled. This was when Holiday Rambler was still building the C's and A gassers for the Monaco brands.
That changed to laminated panel box construction, like everybody else, when the H-R (and other Monaco) brand was put on models built at the recently acquired R-Vision plant.
I inspected Thor, Coachmen, Jayco, Fleetwood, Forest River examples closely, and visited four of the factories, which made me go with Winnebago. But they are not the best, as you can get better construction using either modern or traditional construction methods, from some small RV builders, if you want to pay the price. For construction quality, have LazyDaze build you one.
There is no taking most C's very far from very good paved roads. They are too long, too much wheelbase, too much rear overhang, too little ground clearance to deal with even minor bumps, dips, crowns and ruts. A big part of the house is built in a "basement" hanging down over the sides of an already too low frame.
Short C's do better than long ones, but even short conventional C's will have nearly half the house behind the rear axle to get weight distribution right at maximum weight.
There are important exceptions, like Tiger, the old Xplorer line, and Host Industries' expedition vehicles. You will find these built higher, on conventional cab chassis with higher frames, and with less of the house hanging low under the floor and the frame rails.
I would rather have a truck camper to get to remote fishing areas. It would depend on how remote, are you having to go 2-3 miles from a convenient RV campground, or is your fishing site going to take you 20-50 miles from the nearest facility that can handle the motorhome?
Tom Test
Itasca Spirit 29B