CKK, probably a wise choice considering your planned ventures, to give you peace of mind.
Out west here, there are many many miles even betweens gas stations. The fords 55 gal gas drum it carries comes in quite handy in places such as these. The pop-can sized V10 pistons (well, just about that small), has enough power to pull that house behind it plus trailers, or cars, up the Vail Colorado mountain pass, and others, with ease. And the transmission has engine braking feature, that prevents one from burning out the breaks on the way down. It works very well. As a side note, my brother, a Ford mechanic, has clients that has V10's with over 300-400K miles on them without any engine repairs. They bring them in for oil changes etc. It's an old proven engine. Look at Class A's, that are not a Pusher. What engine do they equip them with. Ford 3 valve V10 (Sadly they can't put the 3 valve in our E Series, because I heard it doesn't fit. :(

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The E Series, is not as modern as the F series by a long shot. Ford just has not kept up with modernising its design.designed. But it's comfortable for me, and actually now after some suspension improvements, does drives like an SUV However, doing it over again, I would have opted to go with the E450, which has a stiffer suspension, and maybe I would not have had to touch the suspension.
As far as fuel mileage is concerned... Salesman at PC, said the improved mileage with the Mercedes would probably not pay back the upcharge that it has.
Just my two cents worth, that I have learned through the years, that gives me peace of mind.
Denny and Barb