I put the roof rack from my old Ford Escape on the back of my P500. I cut up lengths of 3/4" ID heater hose and put them around the Honda rack where the roof rack makes contact. The hose helps holds it in place and absorbs vibration. I secured them together with u-bolts. The u-bolts started wiggling loose pretty fast though so I strapped the two racks together with 4 rubber bungees.
