Based on my aerodynamic expirience, I would think that closed edges are far less dragy than laces.
That's my vote. I've been told by a few over the road truckers the absolute worst thing to haul is the corrugated pipe. Not a lot of weight, but a ton of drag.
Even towing a beach cat, there's a whole mess of drag there, and not much weight. I've put 7 catamarans in a 4500# enclosed trailer and got 12.7mpg over the course of a 2500 mile road trip, I get only slightly better pulling a triple stack.
