I say keep adding more wood to it, make nerf bars, body armor and a roll cage out of balsa wood and see if the truck floats. That way you won't even need the kayaks, you can literally go white water rafting without ever leaving the driver's seat. You could get some paddles and paddle out the window too to simulate real life kayaking.
Personally I don't see what's wrong with making this rack, if I saw this truck at Wal-Mart it probably wouldn't phase me at all. Any of you ever seen a pickup truck with a full roll bar made out of PVC pipe? That is hilarious.