I pull a tall 24' enclosed car hauler with my pickup and thought that one of the "wings" that you see on fifth wheel rigs and on big trucks might help with mileage. Any thoughts on where to get a used one and whether it could be mounted to a fiberglass topper?

Are you talking about a fiberglass or aluminum "wing" ? .... I have an alum one that I am not using ...since I tow with a dually and camper on-top or a classic Dodge motorhome. PM me if interested.

How much tongue weight do you have ?

this kind of thing:

http://www.nosecone.com/aetruck.htm

you might also consider improving the rear end of a blunt trailer too:

http://www.airtab.com/en/

http://www.buyairtab.com/

more scientific info on the general idea:

http://people.clarkson.edu/~visser/research/drag/truck/

don't forget the tow truck

http://tinyurl.com/4ck68d

http://autospeed.com/cms/A_108656/article.html

good luck

The wings do help on the mileage, basicly if you
take a string from the front of the hood to the front
of the roof on the trailer you need to put the top
edge of the wing to intersect the string. If you
can lay the wing over farther and still intersect the
string the better it is. But those wings are pretty
pricey

I assume that the aluminum wing would be best. Needs to attach to the fiberglass "topper" on my pickup. Trailer is extra tall. Tongue weight is 840#

Does anyone know if the fiberglass toppers that raise up at the back help with mialage when towing a car trailer?

Maybe I just need the Christmas Tree

If the topper tapers up in the back and deflects the wind upward it does if your pulling an enclosed trailer as it helps deflect the wind away from the front of the trailer which can otherwise make it feel like your towing a cinder block.

The aluminum wings are nice but when your not towing, the wind still hits that wing and hurts the mileage some vs. not having the wing at all.

My trailer has the extra height and totally flat front.