I use poplar for the gunnels and chines when building smaller boats. I have a 10 ft length of 4" plastic pipe with the cap cemented in place on one end. I fill the tube with water then put the poplar in it and cap the end and let it soak for several days.
I won't suggest that it bends like rubber, but it does bend quite well and shows no signs of stress. I secure it to the boat ribs/frames as I go and let it air dry for several days and it holds it's new shape quire well.
I have not found another wood that works that easily.
Don Dando