For planking we mostly used 20 cm wide foamstrips which works fine. We used a few 30 cm wide strips in the middle of the hull and some 10-15 cm wide strips in very curved sections (like the bow).
We only used a heat gun a bit to bow the foam strips in the large curve near the keel. For the rest the strips could be bent and held in place easily with two (20 cm strip) or three (30 cm strip) screws on each batten.
In the bow section I removed the battens on the flat section just below the gunwale-line. This section should be straight from frames 1-5 (checked this with Ian Farrier). The only way to achieve this is - as far as I can see - to mount seperate battens in the section between frames 1-5 and 5-12.
At the junction of the flat section below the gunwale-line and the curved part of the hull, I didn't try to cut the curved strips to the correct lenght. In stead I just let those strips long, and butted the flat section against them.
Here the grooves between the strips have been filled with putty. The edge at the straight section has yet to be filled. At this edge I'll cut the curved strips to the correct lenght once the hull is out of the mold.