I would look at a trailer like Incredble said. Even to the top of a shell on a full size truck is a reach for most guys, and it looks like the top section of your vehicle is even higher than that. If you wanted to build something to stand on to get the reach you may need, I don't know how safe something would be doing that. When I did traffic signal repairs, I would carry signal heads on my shoulder and go up a 10 foot ladder, and is was a pain when I had to do that. They had the weight, but would only be 4 foot long and I can't imagine carryng a 15 foot kayak trying the same thing. Even if someone thought of carrying a kayak on the side of their vehicle, I think the vehicle code used to only give you 12 inches beyond the side of your vehicle it could protrude and be legal. It's a hard call
Perry