Finished a rendering of the cover in Inkscape, and it looks pretty good. It took quite a while to get the fonts, weights and sizes to match the original, but I'm pleased with it. The output PDF has marks and bleeds, hopefully big enough (we'll need to run it by the print shop). The way I've done it follows the model of the Illustrator structure, but I can now see that a much better approach would be to build the front and back covers as individual groups, and make the spine a separate block, so that it's trivial to change the spine width. I'll do that for the next one. 120 minutes.