To wrap the 4WD issue, as I experienced the resale value in states with dry weather is non-existent.
I spend part of my life in 4-seasons and know that 4WD is crucial in slippery condition, but my present truck is RWD with normal differential and I took my camper on it into some logging roads just fine.
IMHO with camper the front drive will be much useless on rough roads since front wheel will be in the air most of the time. Locking differential will make major difference.
Anyway, can't find comparison in fuel consumption between 4WD and RWD, but assuming 1-2 mpg difference, the extra fuel to carry the option over 50k distance will cost in range of $1000.
Additionally 4WD is adding about 2.5" of height and getting into those Superduties is not that easy and I had to carry in elderly passengers.
So I will consider 4WD as "cheap insurance" that I might never use, but might be good to have "just for 1 in 10000 situations" but it will not be decision maker.
edited for new info and error correction.