Sneeky, I am doing the exact same thing you described. I have used a Front Knox door that swings inward, fire rating 1680 degrees for 90 minutes house fires usually 1200 degrees, cost around $3,475.00, best door on the market if you have the budget for.It has a safety latch on the inside in case of accidental closing. My room will be 19'x6' this is the size of my front porch. The reason for my vault room is,a good resale option,main reason my house burnt down lost everything, (including our Chocalate Lab Chelsea Girl), who we miss dearly. I'm a builder in IL., this is the first time I've done one,so as I build it I'll keep you posted. So far, some info.
1)If you don't have walk out basement need to install before subfloor. Door is extremely heavy 1,200 lbs.
2)Use a backhoe, etc, to lower unit into basement. Need several men to duck walk it into opening, keep strap attached to keep from falling.
3)I will install a land line phone, just in case.
4)Room has to have moisture control, climate control, and ventalation. Need to find out how to keep water and smoke from entering through holes from the duct work, etc. in case of fire. Also, I was cleaning the brick on front of house after brick layers and had a little water leakage. Have to make sure it's sealed from the elements before you finish room. I went in room yesterday extremely cold and damp. Temps here coming out of freezing.
That's about all I have far now. I'll start posting pics if you are interested, and details on design and construction as I figure them out. Let me know.
Joe E Sikora