[Gmail-Users] Backing up Gmail w/o onboard mail prgm?

Hi, is there a way, outside of setting up an onboard mail prgm, to
download all archived mail in my acct so I can back it up offline. I'm
setting up a puter in my home that 3 puters will be tied into, it will
not have a internet connection, but will be tied in via cat6 cable. I
would like to be able to once a week download from Gmail, then transfer
to my backup puter[it will have 1.2 terabytes of storage] TFAI
Randy