If you're going that route be sure to avoid putting anything with gypsum in it inside the safe. Also use a safe that doesn't contain gypsum - a lot of the less expensive ones do. Gypsum keeps the temperature down by releasing water vapor into the air, which is of course not particularly good for metal and some electronics. And bear in mind that in the case of a big fire, you may not be allowed back into the house for half a day, sometimes more than one day. That's a long time for your stuff to be locked in a sauna.Another option for fireproofing and protecting your safe from attack is building a frame around it and attaching the frame to the wall and the floor. I use layers of cement board on the id and od of the frame. You just need to build the walls in sections (leaving the outer cement boards off at first). Get it in place with steel framing and attach the outer boards once it is complete. You can also leave a couple of holes in the outer layer and fill it with foam or other insulation to boost the fire rating. I had one guy tell me at the SHOT Show that he did a similar build but used sand to fill the walls and top.
Build the front extended out a few inches and you can also build a covering that can screw into place covering the door in case of a pending fire in your area.
Having this type of a buffer will extend the fire rating of any safe,