I'd say that with the hub caps you have now, you could get some stout wire and put on some coroplast or pizza pans right to them using the holes. this way it is reversable. people have reported gains from them but not enough to offset the roughly 100 bucks they cost. don't get me wrong, they look sweet so if it's looks you are going for, then have at it.
on a side note: you can get coroplast from a sign shop pretty cheap. I am all for free signs but they are usually pretty small. my local sign shop is going to sell me a 4 foot by 8 foot sheet for $20 which I didn't think was so bad. I am planning on making a partial belly pan out of it. I just looked in the phone book for sign shops and called a few. they cost a lot to print up those things.
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