Due to the length of the item, and related delivery charges, we DON'T include this with the purchase of JET Rack®. You can purchase strut channel cheaply from most hardware stores, such as CEF (here). It is recommended that you use the shallow 21mm variant.
Often purchased in lengths of 3m, you may want to cut it down to size for your van.
A single length of channel would normally cost around £10-£15