It's an interesting idea, but the Humber will be up against lots of other ports and airports and I hope that the political wrangling by the local MPs over the Humber/Lincolnshire LEP issue won't go against any Humber bid.
There was an article in The Telegraph last year about the growth in the renewable energy industry in the Humber region, which stated, "Brexit is not a game-changer. The wind industry has found a loophole. Projects outside the 12-mile coastal limit are technically not in the EU so the components can be imported into bonded-warehouses without duties".
This could be why Orsted opened a base at HUY and Salfina acquired a hangar recently. I'm not sure what other sector would benefit from the airport being part of a freeport - unless they start flying fish from Iceland again?!