Hi Michael, I bought a Thule Velospace XT3 with extra bike carrier, and a Thule Backspace luggage box that fits on the carrier. This is a tow bar mounted solution. The Backspace is basically a large waterproof storage box. We use it in the summer to put our inflatable kayak in and take it to the beach. With the Backspace fitted you can only carry 1 bike. Without the Backspace you can carry 4 bikes. Expensive solution at around £1200 all in but very versatile. Another good point with the Thule Velospace XT3 is that you can tip it backwards while loaded and still open the tailgate of the Alphard. Only a few towbar bike carriers can do this.