Your suggestion sounds a lot like the airbases in Civ II. As for having these bases on road, do you mean that it has to be connected by road to your civ? I found that airbases in Civ II were handy on islands, so that they can't be connected in such a way. Considering this, maybe such coastal airbases could incorporate a harbour to connect with your other coastal harbour cities.
As for a trading structure, I fail to see the use if it is already connected to the rest of your civ. The only way I see a benefit is if you build one while not having any city-based airports at all throughout your civilisation.
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