I'm a big fan of cummins dodges as well. I really like mine, and so far it has been the most reliable four wheeled vehicle I have owned(my suzuki bike edges it out as most reliable since it had no problems, ever, while the truck had a transfer case leak), I actually dislike the 94-2002 trucks, I just can't stand the interior. I prefer the obs trucks and their wing windows, different strokes for different folks and whatnot.
That said 20k for a 35k truck may be a good deal, but it still doesn't make it the best choice. Because of his preferences for what he wants out of a vehicle. Not wanting a loan is just as important as wanting a back seat imho. Personally i think the main attraction to a diesel goes away once the electronics are involved, and the mpg drop below 15-ish something that mega will both suffer from.
Fixing the ramcharger is your simplest option, you change very little, and it you decide you don't like it later it is not the end of the world because you wouldn't have much invested. Seems to make sense to me.
Have you considered just getting any old work truck for a work truck, and then pocketing the difference? It wouldn't help your road trip requirements, but if you wanted the stipend, that would be one way to do it. Do you need 4wd? 2wd 2000-ish 3/4t gas reg cabs are pretty cheap lately. Not sure that would improve anything but its an idea.