Fuel cell box ??

[67 455 Bird ragtop]

I have a 15 gallon fuel cell I'm getting ready to install. It's made from .100 thick 5051 aluminum. It will be mounted between the frame rails. Should I build a steel box to go around this cell to protect it from road debris ?? What gauge steel should I use ??

[67 455 Bird ragtop]

Car will primarily be street driven.

[David Pozzi]

If it has no bladder inside, then I'd call it an aluminum fuel tank.
Aluminum melts at 1100 degrees, steel melts at 2500 degrees. In addition, steel has extra protection from debris damage. I'd check for what is common for racing use. I think it's .035" thick cold rolled steel.
FIA requires .036" steel, or .095" aluminum, so your .100 thick aluminum is OK, but I'd add a flat sheet of steel for the bottom.

I was witness to a tractor fire. It had a plastic belly tank with 30 gallons of diesel. An electrical fire started under the deck, just above the fuel tank. The tank started to melt and when it finally blew out it dumped all the fuel on the ground under the tractor and it really took off! We had used up 3 or 4 fire extinguishers before the tank burst.
Any aluminum castings like timing cover and oil filter mounts just melted away. So I'm thinking if you spun out and hit a guard rail or got rear ended, and a fire was in the area of the tank, it would drop all the fuel out as soon as it got very hot. A steel enclosure would buy more time, but fuel is still going to boil off.

[sam 74]

when i ran an aluminum fuel cell om my last car i mounted it between the frame rails and used a box, i heard it take a few rocks a over the years and i never regretted having it.