How about generating your own bitcoin keypair ?
Have a look in github and you will find several ways to generate bitcoin private key and public key. Then just send what you mined to that address. they will be stored safely but you should print a page with the content of the private key, and a qrcode, just in case your computer gets hacked, burned, demolished.
Then when you want to spend them, just follow this guide :
http://bitcoin.stackexchange.com/questions/5941/how-do-i-import-a-private-key-into-bitcoin-qtwhen your transaction gets ~6 confirmations, you can then destroy the wallet.dat file, this way no one can access the wallet.
Re import when needed.
You can do this with ETH also from a browser console, or a terminal, so your datas are always safe as you don't provide your private key.