Jason,
If you think you won't have any trouble installing it, that sounds pretty good.
If you are concerned about the fire rating, you can cover the safe with sheetrock or even make a full framed, insulated and sheetrocked wall surrounding the safe.
The difference between a fire rated safe and a safe that isn't fire rated is just a layer of sheetrock inside the safe. Sheetrock outside of the safe should give you similar protection.
For any one that's curious, the $400 Sentry safe has sheet rock. The door is 1/4" thick I think. The hinges are hidden, there are plenty of bolts (I think 8). The body of the safe is pretty thick also. It would take a real safe cracker or a really determined amature to open it.
When you think about the value of the safes content, you should also consider who you are trying to protect it from. Fire is a valid concern, it doesn't discriminate. I don't think a real safe cracker would take the risk to steal my collection, stealing a Mercedes would be easier and much more lucrative. Some crack head might think I'm a good target but I doubt they will be able to do anything beside tip over the safe. I doubt any one stupid enough to target me could get the safe to the top of the stairs without someone seeing them, then they would have to push it down the stairs which would create a real racket.