I have built a LOT of aluminum fuel tanks for commercial fishing boats. Mainly in the 300-450 gal. size. I like to use 5086 alloy, versus of the standard 5052, alloy because the corrosion resistance is better.
Of course neither a gasoline or fuel engine likes water. Aluminum is a better conducter than Steel and therefore Aluminum creates more condensation than steel because of temperature changes. It is also very important to have some nicely fitted and solid welded baffles inside an Aluminum tank for structural support. Because of the condensations issues w/ aluminum it is imperaritive to use a (gasoline) fuel/water seperator.
Also, if you're not famaliar with putting two different metals together, steel & aluminum I'd recomend doing a little research. Pay specific attention to your mounting system, any type of "rubber" pad for the tank to sit on versus directly to the steel frame is a good idea. The threaded penetrations in aluminum can be an issue also, they gall or corode easily, always use some type of pookey on the threads, gray colored anti-seize is about the best. And lastly, if you're in a salty region and/or drive the Bronco on roads that have had salt applied to them you should use a Zinc as a sacrificial anode to combat the salt from eating your aluminum.
The highly polished aluminum tanks you commonly see on semi truck are a totally different application then a bouncy little Bronco, that may be used off road, and the rear tank may hit the ground occasionally.
I use a steel gas tank, and a steel skid plate on my Bronco........
