I was looking into installing one of those incorporated with a toolbox to take advantage of cheap diesel when we find it.
Rds tank toolbox
RDS MFG INC 72746 Fuel Tank
https://www.amazon.com/dp/B001HVHO82...53KKGC552AW5MS
I have read there can be issues with some states auxiliary fuel tank regulations. I have not researched that part yet.
For this next road trip, I'll be taking two of these
No-Spill 5-Gallon
https://www.amazon.com/dp/B000W9JN4S...FK6FE9C0TTC8AV