We're headed out on a road trip today, looking forward to seeing some gap-filled MPG.
Mostly this is coroplast, some aluminum ribs to give it curvature where required. Bought a 1ftx3ft cut of neoprene rubber at a local industrial hardware store. Used that to make some custom gaskets facing the car (not perfect, though they happen to look good in the resolution presented here, but a few ~0.5" gaps in places).
Sorry, you can just barely see it here, but there is an aluminum sheet to shape and protect the coroplast above the exhaust.
To facilitate articulation (when the box hinges up), the underside is restrained with clips.
It also tucks under the hitch receiver.
When the box lifts the under-panels can pull away from the car but don't snag on anything when they get pushed back in.
One 'gasket' is actually a strip that velcros to the top of the bumper.
I need to paint the coroplast to prevent UV degradation. One issue is that the coroplast deforms under sunlight if it's painted dark. This was noted by kach22i (
http://ecomodder.com/forum/showthrea...tml#post375743), I've also noticed the problem on my black coro Corolla wheel skirts. The gray paint already on the box is also too dark (pretty sure). So I need to either rebuild the structure in a better material, or paint the whole box white.