I would want something more heat tolerant than a ziplock baggie. In a fire, those would melt inside your fireproof safe, destroying your documents with melted plastic rather than heat charring or water damage. "Fireproof" does not mean "nice and cool inside". Typical rating temperatures are 350 degrees inside the safe. Ziplock baggies would be toast at that temperature. Maybe put your documents inside a cardboard sleeve, then put THAT inside the baggies. So in a fire the cardboard would stop the melting plastic from touching your documents.