I added a NOS Blazer 26 gallon diesel tank from Coleman's Surplus to my '85 Toy 4runner. I can now carry around 45 gallons of fuel plus the 5 gallon jerry can. I installed it behind the axle where the spare tire used to go.
One pic:
You can just barely see the bottom of the tank skid plate (1/16th" sheet metal) in this pic:
I use gravity feed (ignore Transfer Flow and their bogus "gravity feed is illegal" bull crap) going through a 3/8" in line fuel filter and a 3/8" ball valve from McMaster. I only "refuel" while stopped not while driving.
Hope this helps.
Al