I've already got a toolbox, looking for a tonneau cover that will work with it. It's a 11 super crew with 6.5 box. Found an extang on bay for $289, wondering how something like that will hold up. Any input is greatly appreciated, I need frequent box access, my main reason for wanting one is improved milage.

 

Improved mileage is more than likely just a marketing ploy by the companies. I have no noticeable mileage increases since my cover has been on since November.

Are you looking for a soft or hard tonneau? There are a lot of options out there depending on your tastes and needs. Soft, roll top, folding, etc. Also depends a lot on your budget. But again, if mileage increase is your main objective...then you're likely to be disappointed.

EDIT:
Is your toolbox flush mount, or mounted top side of the rails? There are some nice options if it's flush mount.

 

Its on the top of the rails. If i'm not going to see any increase in mileage i'm not going to spend the money. I asssumed the drag of the tailgate would kill mileage, my F350 gets a few MPG better without the tailgate on the highway.

 

It's a debateable matter. From what I've read, the shorter the box, the less likely you are to see a mileage gain with a cover. You might see an improvement on a 8' bed, but I can say first hand that I have NOT seen the 10% gain on my 5.5' bed, or any gain for that matter.
There have been many tests on this topic. Seems that tailgate down is bad, tailgate removed can be beneficial but also illegal in some States, and that tailgate up with no cover creates a spiraling turbulent effect that actually swirls enough to push the airflow over the bed and tailgate.
I bought a cover to keep the elements out of my bed, since it's used like a trunk on many instances, and for that purpose it works well.

 

Hmmm, i'll have to do more research. Thanks tho, you may have saved me some $$. In reality, i'm a contractor so it's not overly practical, but i was hoping the fuel savings would make it worthwhile. I guess not.

 

I have had tonneau covers on almost every truck Ive owned, and can honestly say that it provided no increase in fuel mileage. I didnt really care because i purchased the covers simply to keep my personal items out of the weather when traveling.

 

Additionally, you would only see an increase if you were at highway speeds or higher. You won't see a benefit in town.

 

You won't see an MPG improvement with a cover. If anything, it'll hinder access to the tool box. I put one on my ranger since I needed a large dry space for transporting musical instruments and other things that can't get wet. I saw no improvement in MPG but didn't get it for that anyway.

Plus, I think they look tacky with a tool box. For me, it's one or the other

 

90% of my driving is highway, thus my thinking it would be beneficial.

Thanks for all of the input guys, made it an easy choice for me.

 

Mythbusters did a show about this a couple of years ago and found no increased MPGs with a cover. YMMV.