I have a canoe and it takes 5 minutes at the most. I lean it up against the Roof rack. I use an aluminum pole, about 6 feet long with a clamp at one end. I clamp the pole at the back end of the canoe, then I lift the back of the canoe up and plant the pole on the ground, the wife just keep it steady from falling. I go on top, pull on the canoe and while I pull and bring the canoe down on top of the camper, the wife pushes up with the pole to bring the back end up, very easy to manoeuver. I then attach the canoe to the rack. I also installed two round attachement at about middle of the camper so I can attach the canoe at the front to. The front end is sitting on top of the camper with a piece of foam.
Taking down is just the same reverse procedure.