The pre smogged diesels will be loosing their value at a greatly increased rate as they become older and worn out. Their features and creature comforts are now getting very far behind the newest offerings. To move any load be it shopping cart or camper the heavier the load the more energy it takes to move it. Diesel vehicles are not exempt from that law of physics. Modern diesels are suffering greatly in their fuel efficiency compared to the older engines.
Actually no, that's not the case at all. When you actually use diesel engines the way they're intended to be used (towing, hauling, driving under load) the modern diesel engines do just as well, some do slightly better, relative to their predecessors. The exhaust temperatures are high enough in that type of driving that the DPF is able to regenerate mostly via a passive method (no extra fuel consumption is need to burn off the soot). The DEF gets consumed at a higher rate, but that extra cost is marginal over annual driving.
Stop-and-go city driving, yes modern diesels may see more fuel consumption due to the emissions systems. But if you're driving around a heavily laden diesel vehicle (like the OP's sportsmobile) for long distance trips, there should be a marginal efficiency penalty, if any at all.
Pre-smog diesel vehicles are generally losing their value (as most vehicles do), but the relevant caveat is that they are much slower to depreciate in comparison the gasoline variants. Moreover, I believe the OP is looking for an engine, not pre-smog vehicle. The vehicles from that era are starting to fall apart...the engines themselves are able to run for many more hundreds of thousands of miles, given the appropriate maintenance.
For overlanding in the US and Canada the cost discussion is usually secondary. The most relevant factor is usually range. If you can achieve your desired range in a gasser by carrying extra fuel, that might be the best option for you. You will not need to carry as much fuel to achieve the same range with a diesel. This is always a factor on the trips I've been on. The difference between 8-9 mpg (gas) and 13-15 mpg (diesel) on the trail is huge.
^ This. Comparing two vehicles (one diesel, one gasoline) that are otherwise the same, the diesel will get somewhat better range due to its higher efficiency. To some, that may not matter. To others, it may be the deciding factor and worth the additional cost.
And BTW, some of these discussion points are not exclusive to North America. In places like Australia and South Africa, the famed Toyota diesel LC's and Hilux's do in fact cost more to buy and maintain relative to gasoline 4x4's. The 4x4 market trends towards diesel in spite of that cost discrepancy because 4x4 owners prefer the low-end torque and efficiency provided by the diesel as well as there is extensive logistical support for diesel vehicles in those areas. In North and South America, there is extensive logistical support for both engine types. You just need to be aware of fuel quality and/or take the right precautions (fuel filter maintenance) if traveling with a common-rail diesel outside of the US and Canada. Any diesel engine post 2011, with EGR, DPF and SCR, you're better off avoiding Mexico and the areas south of it until they switch over to ULSD, which will likely happen at some point.
