Drawing a double helix in Inkscape

I've seen this How can I create a double helix? question but I am here to ask you how to create a double-helix in Inkscape, instead of illustrator. I have tried to achieve this via creating two sine waves (using the Parametric Curves extension) and doing some cutting and colouring-in from there and this is what I'm at atm. After this I would create another sine way with the opposite vertical orientation (which would be the second helix) and go from there.

I have also tried (and failed pretty miserably: I find it impossible to seamlessly vectorize such complex raster files) vectorizing a structure of DNA drawn using Accelrys DS Visualizer (see below for the original image if you have the skill to vectorize it in a way you could share with me). I would like to know is there any better ways of doing this.

This is what I have so far from the sine wave method; see in the first instance where I wanted to colour between the waves, the coloured area would form part of the helix.

This double helix is the one I obtained using Accelrys DS Visualizer, with later GIMP editing (mostly in an effort to make it easier to vectorize, you may note that the helix backbone is no longer coloured in shades of white like it was originally).