Fireproofing My 22gal. Fuel Tank

[SCHOONER]

Hi Guys

I just ordered a 22gallon fuel tank for my 1966 fuel tank. My car holds only 16gallons. The 1970 fuel tank fits my '66 so I got no problems with installation.

THE QUESTION(S)

How and what do I use to FIREPROOF my new fuel tank?

What I intend to do is:
Make a 18gauage sheet metal box to cover the new 22gal. tank. Mig weld it all around the new tank. However, before I do that I need some info from you guys on what and where can I get a FIREPROOF MATERIAL to lay on top and around the sides of my new fuel tank.

And then of couuse seal (mig weld) the entire top sheet metal box.
I will not do anything till I hear from you guys.

THANK YOU ALL AND GOD BLESS ALL OF YOU.

Schooner