i have a lowe aluminum canoe and it has plastic seats with a bit of contour but no backs on them. the rear seat is close enough to the back of the canoe that i cut a piece of foam swimming noodle and stuck it on the crossbar behind the seat and did the same on the front seat. the foam sits just in the small of your back if you lean back(or sit toward the back of the seat), doesnt weigh much of anything, and doesnt interfere with paddling. it also helps to keep things cool instead of the aluminum getting burning hot in the sun. just a thought