Thanks for the pictures. So it's not about the skin as much as the framing. 1/4" ply would be heavy, consider luan paneling (cheap) or marine plywood ('spensive). Here's a chart that lists 4 materials available in 1/8" thickness:
Plywood Thickness | ThePlywood.com
You might could use steam to bend the curve. If you wedge the shape, tumblehome will increase from front to back.