What I’m wondering is do I really need a fan?

I’m thinking I could catch air via an NACA scoop and use that instead of a blower.

Yeah; I guess if you use a scoop to force the flow from outside you shouldn’t need a fan.  I chose to recirc cabin air, and I use a 5-6” centrifugal that I gat cheap at Lincoln surplus – it blows a lot of air.

But wouldn’t you like to get some heat going while you’re on the ground?

Al