DIY Roof Rack Cargo Box for any car rack system (yakima, thule)

This post will show you how to build your own DIY roof rack cargo box.

Roof Rack kits are way overpriced. The companies who make them gouge your wallet by selling everything separately and for much more than they need to be. Even on ebay, used prices for rack kits are expensive (doable, but IMHO still expensive), and if one wants to go beyond just the typical roof rack, and add say a cargo box, the initial cost of doing so is almost $700 brand new!

So when my wife and I had our first child (boy, 6 lbs 5 oz. born nov 18th), we quickly realized that we needed more space in our car to carry the usual odds and sods that babies tend to need while out and about. So our dilemma was either to get a larger used car (10k etc.), or to get a rack system (sub 1k) and see how much space it would provide us. We opted to try the cheapest solution first.

Finished Cargo box and Yakima rack installed

Finished Cargo box and Yakima rack installed

I picked up a set of yakima crossbars, 6 lock cores, and Q-towers off craigslist, and purchased the correct Q-clips from rei and another sale off craigslist (to build the base system for my corolla, one needs crossbars, q-towers and q-clips). The total came out to be $190 for all of the above (new would be around $375), still expensive but acceptable. After initial installation and test drive, the next step was to stop the obnoxiously loud wind noise which was created by the crossbars while traveling faster than 35mph. A quick google search turned up that to do so cheaply (meaning not buying the $70 wind fairing), all one had to do was to take a thick nylon bungee cord ($2) and twist it around the bars (car manufacturers use this same principle on their radio antennas to alleviate wind noise as well). This worked beautifully, as all wind noise caused by wind running through the crossbars was eliminated.

After the base rack system was installed and all obnoxious side-effects minimized, it came time to “build” the cargo box which would hold some of the bulky objects one would pack for a weekend getaway. Fortunately, I found a suitable container at work. It was a used Abex pop-up exhibit travel case which was somewhat aerodynamic and made of durable plastic since it was made for shipping and travel. One can pick up similar shipping cases (which do not need to be abex branded) for pretty cheap off ebay, I did a search and found them for about $50-100 with shipping included (search ebay for ‘shipping case’).

I then purchased two 1″ x 1.5″ x 0.125″ T6061-T6 extruded aluminum tubes cut to 36″ long (my front crossbar distance from the rear crossbar is 32″)  from ($30), and some U-bolt hardware, 2″ bolts, stop-nuts, and large fender washers from lowes ($16). I was pretty impressed that the U-bolts fit the yakima crossbars perfectly and snugly. I then measures and drilled 4 holes in the aluminum tubes to run the U-bolts through, did a test fit on the rack crossbars for fitment, and then proceeded to mount the aluminum tubes onto the cargo box.

This picture is with the cargo box already mounted

U-Bolt and Aluminum tube Installed

I eyeballed the placement of the tubes onto the cargo box, and drilled two more holes for each aluminum tube. I then marked the centerpoint of those holes onto the cargo box and drilled four holes into the cargo box. These four holes would allow me to run the bolts through from the inside of the cargo box through the tubes, and allow them to be securely attached.

All four bolts and caps installed through and secured

All four bolts and stop-nuts installed through and secured

Bolt, fender washer, and nut installed

Bolt, fender washer, and nut installed (added electrical nut to protect car paint in case it hits top of car).

Top of bolt and large fender washer inside cargo box

Top of bolt and large fender washer inside cargo box

After the installation of the bolts, the cargo box needed to be weatherproofed a little. I used some door weather-stripping that i had laying around and lined the lip of the seam where the cover would butt against. After that, the cargo box was finished!

Cargo box mounted on yakima roof rack (notice the white weatherstrip installed)

Cargo box mounted on yakima roof rack (notice the nylon bungee cord wrapped around the crossbar. I doubt it needs to be there with the box mounted since the box would stop the wind from whooshing over the bars. I was just too lazy to remove them)

I have since taken a trip to Tahoe in the middle of heavy wind/rain/snow/freezing temperature storms and have yet to have the cargo box fail on me. The four bolts with large fender washers securely hold the box to the aluminum bars. The weather stripping keeps the water and snow out, and the box is aerodynamic enough to keep my gas mileage at 28mpg (without passengers/cargo I get about 30-31 mixed driving. The mpg hit might be because as I was carrying 5 passengers and their cargo as well). The wind noise is very acceptable, and just noticeable at speeds of 75mph.

Box taking a beating

The cargo box in some harsh conditions

Overall, for saving some money, this is a project that is well worth it (spent less than $250) . My sister in law even mentioned that she thought it didnt look any worse than commercially built cargo boxes and worked just as well!

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15 thoughts on “DIY Roof Rack Cargo Box for any car rack system (yakima, thule)

  1. Giles

    While I certainly agree that the rack systems are ridiculous… So is strapping an oil drum looking thing to the top of your car. I can’t imagine what sort of forces are being exerted on your roof but I’d say it’s borderline dangerous to have such a completely non-aero blob sitting up there.

    With a little looking you can find a used cargo box for less than 200.

  2. Blog Master Post author

    True, this thing is pretty ugly. However, the dimensions of the box is about the same as the yakima factory boxes, it just doesnt have that nice front sloping curve. Its only about 15 inches in height so the aerodynamics of it are not too bad. I still get great gas mileage with it on, if thats an indicator of wind resistance/aerodynamics. The rack can hold 110lbs of weight, i probably put 40-50lbs max in the box, so safety isnt much of a concern.

  3. David

    Creative, the square design strikes me as odd. Something I personally would have never thought of. Thanks for being the pioneer. Its great that you only loose 1-2 mpg, with air dynamics working against your construction a larger drop in mpg seems much more likely, having this thought was what really kept me thinking I had to have some egg shape container on top. :cheers:

  4. wolffe

    certainly is unique; I don’t think I could drive that anywhere with a straight face.

  5. John

    I would just make an air deflector for it and you may get your mpg back; it may be better than it was to begin with. Hey, I am not going to be one of the people that are criticizing you over this, since when you have a family, you do what you have to do!

  6. Fred

    There’s no way you’re only losing 1mpg with that monstrosity strapped to the roof of your car at highway speeds.

    I found a nice Thule box for 180$ which only needed one fiberglass patch. I lose about 4mpg with it on the roof going 75 on the freeway but need the space.

  7. Blog Master Post author

    I know, it looks like death, but honestly I compared the mileage between fills and that’s all it went down. The box itself isn’t very tall, and the curved front and rear may have something to do with that. I even had 5 people in the car…

  8. lisa

    dude glad it worked but if you EVER come to FLORIDUGH
    those highway state troopers will be checking your sleigh
    -for dead bodies!!! seriously I am surprised you haven’t been pulled over

  9. Merlin

    Extremely clever; you are a great problem solver! Who cares about the looks. Some people are so sarcastic on the web. This is McGiver 101. Excellent! I am about to make my own roof system and your page was the first one opened from my google search.

    I am leaning towards some heavy duty rubbermaid type containers (plastic chests) with heavy tarp wrapper inside around my contents. The only thing I am not willing to trust is the connections being just washer and bolt/nut. I want to spread the shear force across a larger area.

    But you are inspiring! Thanks.

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