Just did this today... thought Id post it as my first hello to the forum. The total cost of the aluminum was about 12 bucks at home depot and another 12 bucks for the bolts purchased from ORS Racks Direct at this link

No need to shorted the alum strips... just drill holes in where you need them. The hold is super strong...

 

Can you explain what the aluminum bars did?

 

You need something to bolt too.. the ORS Direct Rack bolts just aren't wide enough, so I needed to add a bracket of some sort. The aluminum bars are great as then fit perfectly into the channel of the bmw oem cross bars and slide in. You have to drill holes into the aluminum bars where you need your accessory to mount. Let me know if you need any more information... Its ridiculously solid and rigid... a lot better then some plastic piece.

 

But I do recommend the ORS bolts for this project as they are nice quality... you might be able to reuse the THULE bolts you already have as well though if they aren't too long...