FRS and GMRS is great for down the block but NOT for unknown distance and terrain.
Please just get your HAM License and use equipment that is designed to be used at distance and that have repeaters.
FRS and GMRS with limited Power out and Antenna (the most important is ANTENNA) just makes communications under a disaster very limited.
I have FRS / GMRS radios for the neighbors or for a buddy who may be posted at the end of the block or with in a RV park. They are great for this stuff and that will work with others who ONLY have this tool.
But the Limitations are vast and thous of us who wish to have solid communications need to get a HAM License.
Scott