I built my own. , ordered a door.
This stuff here, is what you want in between layers of type "X" gypsum, and some 1/4" steel.
https://www.amazon.com/dp/B00ODP54FY/?tag=accuratescom-20
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It's rather expensive, but when installed correctly, overlapping seams as instructed, it is designed to contain fires that may start inside grease hoods in restaurants. So literally , this would be the only thing left in the smoldering remains of a house.
Building it indoors has it challenges, getting my buddies welder inside, and hauling all the steel to set up the door frame was a PIA,
I boxed mine into an unused closet, on an exterior wall, so nobody can get to either side .. If they want in, they'll have to work for it.
The front frame ended up being over 13" thick, by the time I put the gypsum, steel plate, fire wrap, cement block, and 2 layers of gypsum inside.
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Inside of closet is 3' x 5' deep, and over 72" tall, so you could easily move around inside, I also ran a supply and return duct work into it, so it gets heated, and air conditioned year round, along with a dehumidifier that sits at the back wall, .
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It's too bad I lost all them rifles in that canoe accident though,
You could also build a room in you basement like that.
