Get a USB stick of 32 or 64 gigs with a live version of Tails on it, encrypted. Download the whole blockchain manually.
That's about the only way you can be sure that your coins are safe. DON'T FORGET to have a paper wallet, USB sticks can randomly fail...!!!!
The better option of this would be to just use the electrum on tails and remember the seed or allow it to be apart of the encrypted permanant drive on tails. Especially since electrum is already setup to sign offline transactions. Then make paper backups of the seed.