You could move it around the park with the most anemic 3/4 ton made, but the X country trip is another thing.
Assuming you’re the better part of 20,000lbs, that’s a miserable (but doable) trip with an old diesel unless it’s tuned and built trans etc. it’s not even worth thinking about a gasser for the big trip.
I think you’re on the right track. Find the right old economical diesel and when you’re done with it, it won’t have lost any value really.
Depends what your overal goal is. After a year and x country are you done? Trailer parked or sold or what’s the deal?
I’m all for getting by with the minimum but the minimum here in an old truck is one that’s built, not stock, IMO.