I have these boxes:
SUV Utility Box
I installed them onto the side/front rails using big enough bolts to fit in the rail w/o turning. I have since changed out my side/front rails for shallow unistrut to take advantage of the many off the shelf attachments available. I will get a pic posted up soon.
Also, I believe you can mount the small boxes on the front rail but I would make sure to attach the short side of the box to the side rail also to prevent too much load being applied to the factory front rail.