The foam blocks should be fine. Especially if you use the hitch to support one end as you can use all 4 blocks on the roof to support just one end of the canoe. As for securing it I would use ratchet straps around the canoe using the in bed anchors. The rigid unibody construction of the RL allows you to rest something on the cab and secure it to the bed without the worry of twisting or movement between the cab and bed. Try that with a "Real Truck".
