One of the "tricks" I learned from my planking attempts with the Saint Malo and am going to use again on the Jolly Boat is to trace the shape from the 1:1 picture that Artesania helpfully provide and then to use this to make a simple planking jig by lightly nailing along the hull line at appropriate intervals into a scrap piece of plywood and then using a planking strip to add the nails on the other side of the plank in the spaces between the first nails necessary to hold the plank while it "sets" into the required shape. I found that after a 5-minute hot water soak and then couple of hours in this jig, the planks held their shape and made gluing a whole lot easier.
Tried to attach a couple of photos of what I have just done but for an unknown reason the upload failed.
A simple and cheap work around. Hope this helps somebody else having trouble.
Cheers, Clive