SPARKY - -
You are right, keep it simple with some 4 x 8 plywood and a fan.
If my future liner is say 3' high and about 2' wide the plywood tunnel would work for size. Being from Florida, I have a few friends that have airboats. So the attic fan would be small potatoes. One problem would be since the airboat "pushes" the air, I would prefer to pull the air through as you mentioned. Why, I don't want the turbulence from the prop and wire cage around it. If the air is pulled through, it brings in uniform air flow uninterrupted to give my yarn tufts fresh air flow over my liner body. I might need more plywood to place the airboat in the pull through zone.
I could have small windows in the plywood to take pictures and video at speed. Plus, I thought of a couple of bathroom scales, one under each wheel to view down pressure. I bet I could do it for under $80, not counting the favors to my airboat friends.
I might even put a few yarn tufts on the insides and inner top of the plywood to see if there is any trails out there or a rooster tail?
If it all works out, great. If not, at least I found out something if I can find all that plywood. But if it's good, I might even apply for the "Good Garagekeeping Seal of Approval,"