That is not an offline computer.

One option is to use Electrum. Put wallet on this offline Macbook (that is ALWAYS offline) and watch-only wallet on normal computer, then sign transactions with a transaction file through USB stick. See docs for better explanation: http://docs.electrum.org/en/latest/coldstorage.html One could argue putting USB in offline Macbook is still a risk, but IMO a smaller risk than your solution for an "offline wallet".


edit: of course your solution is still more secure than average wallet out there.