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.