Ask HN: Tips to build an OpenBSD Thinkpad for airgap use?

I'm interested in setting up an airgap machine. My gut says I should run OpenBSD on a ThinkPad and just figure out all the dependencies. Tails sounds good too, though that's a slightly different problem. I want a permanent system. I just don't want it on the network much and I do want it to handle protocols well. Seems like OpenBSD is the way to go in that regard. But then, I'm definitely not an expert.

There are any number of gotchas to managing an airgap machine though, and there are any number of problems with installing a new OS on a laptop. Wanted to solicit for opinions while I wait for my copy of Absolute OpenBSD to arrive.