What type of kayaks? Are you planning on using saddles or stackers for the kayaks? Planning to take the kayaks off the rack when in camp to get sun? Shouldn't be too hard to come up with something, but you want the panels recessed below your kayak supports to make up for curves in the kayak that hang below the supports. Maybe something below the supports that tilts up or slides out? With kayak stackers, you could have two kayaks on one side and still have room on the other side for panels.
I'm more of a fan of suitcase type solar as you can park and move the panels as needed when in sites that have obstructed sunshine.