" Also, I keep hearing warnings about driving diesels in European cities, but can’t find any evidence that supports the assertion. From what I can see, most of the proposed legislative changes don’t come in for 5-10 years. If you have additional information, please post it in response. "
Well, than you need to up your research as many restrictions apply. Clean Air measures are everywhere. Paris bans older diesels - soon all - inside the Ring Road like many other cities, Holland has many bans on older diesel - often 15 years but varies per city - Germany has basically restrictions everywhere. Depending on what you buy (age, Euro.) you will get restrictions. But most are for cities so one parks at the outskirts and walks / buses / etc. in.
Plenty of choices in France - please observe that a vehicle not registered as a "camper" will cause problems these days when going for the CT or at a traffic stop. It will need to be "VASP"and registered as a "Camping Car or Caravan".