Ethereum is an account based system (not like Bitcoin UTXO), so cold storage is similar to paper wallets in Bitcoin. All the steps are almost the same, the best wallet for this is
https://www.myetherwallet.com and you can connect it to the Trezor device.
The only difference is that you do not need the master public key, but rather copy the address and search for it in any block explorer such as Etherscan.io.
Thanks, I have tried myetherwallet, again and again. I found that MEW Offline version was like a cold wallet, but could not connect to Trezor or other kinds of hardware wallets. Its online version could connect hardware wallets. Ethereum offline version is also a cold, and could be connected to trezor. So, there are two defense lines, and it is quite safe. MEW wallet can not do it. Am I right?
Your steps aren't completely clear to me. Just to clarify - you are connecting your Trezor only to your airgapped computer and interacting with it via Electrum, signing transactions on your Trezor, and then moving those transactions from your airgapped Electrum to your live Electrum to be broadcast?
That's certainly one of doing it and is very secure. An alternative solution for the future would be to use a hardware wallet which is already airgapped and does not need to connect to a computer at all, such as a Passport.
Yes, that was what I did. I do not find a similar method for USDT or USDC. Maybe I have to use online versions for them. Two hardware trezors are used only for BTC with airgapped method, and two hardware wallets (Ledger and Trezor) are used only for USDT and USDC through a third-party software, like MetaMask.
Well yeah, you could also die without multisig and it would be the same IF you don't write recovery instruction letter for your wife.
Making more complications means it's going to be harder for anyone to recover your coins.
Yes, I must prepare one for her, immediately. The airgapped method with electrum software and trezor are quite safe for BTC. I do not have other asset, for the moment
. Maybe I will consider multisig wallets for USDT and USDC two years later.