I'm reading on Baja Nomads that they have ULSD down in La Paz now. This is great news. Also I found a place in Santee that installs auxiliary fuel tanks on sprinter vans
$2200.00 for a 20 gal. tank , $2200.00 14 gal. tank and I think $3500.00 for a 35 gal. tank. The 20gal. tank will go on one side of the van the 14 on the other side and the 35 gal. go's where spare tire is. These are great options. I have been told recently that nobody did extra fuel tanks anymore so I kinda gave up. If they can get them made for sprinters, they may make tanks for other vehicles.
https://agileoffroad.com/
Bajanomads.com