I want to build a custom interior for a gun safe with a some degree of fire rating (Liberty Franklin Series).

Safe stock interiors appear to be carpet over particle board, but I assume that these are special types that will resist heat up to some degree.  

Ignition points being what they are should I worry about doing something heat resistant, or just use plywood (etc...) available at Lowes/Home Depot?  If I have to go to the extreme, Hardi Backer looks to be a good plywood replacement.

The primary purpose of the safe is security, but I'd hate to ruin what fire protections it offers by putting kindling in there...

Use drawer or shelf liner. You can buy it at walmart. Works great for keeping guns & stuff from slipping off carpet or getting scratched by metal.

Crushed velvet.

Fire rated safes have what is essentially drywall on the inside and a carpet like material over that.

If you want it to look nice, and want to build a rack/shelf type unit, use hardwood - maple is a little more fire resistant than most woods (obviously up to a point).

If you don't care much about how it looks, you can use fire rated wood/plywood. The wood or plywood is treated with a salt type substance that gives it a one hour fire rating. Commercial buildings are usually required to use this stuff. It will be harder to find and definitely more expensive, but this could be your best bet.

Quoted: Fire rated safes have what is essentially drywall on the inside and a carpet like material over that. If you want it to look nice, and want to build a rack/shelf type unit, use hardwood - maple is a little more fire resistant than most woods (obviously up to a point). If you don't care much about how it looks, you can use fire rated wood/plywood. The wood or plywood is treated with a salt type substance that gives it a one hour fire rating. Commercial buildings are usually required to use this stuff. It will be harder to find and definitely more expensive, but this could be your best bet.

Thanks for the info on the fire rated plywood.  However, I'm not really that stoked about putting a salt based product in a safe with a bunch of carbon steel.

I think I might go with your maple suggestion though...

If you want the wood look go with drywall and cover it with 1/8" Oak, Ash or Birch plywood.
You can make the shelves of solid wood.