I use a plaintext editor to write xhtml+css, and 7Zip to go directly to epub. I made a blank epub template with 50 empty chapters in it, so when starting a new

I use a plaintext editor to write xhtml+css, and 7Zip to go directly to epub. I made a blank epub template with 50 empty chapters in it, so when starting a new book, I copy that and write new IDs and strings to the metadata, and if I finish it, I delete the unused chapters and remove their entries from the metadata files. It's easier to delete empties than add new chapters, and doing the metadata by hand ensures there's no auto-generated cruft in my file. For illustrations I use Paint or GIMP or Inkscape, but the template doesn't have more than just a cover image in it. After testing various ebook readers, there's no way I would recommend xhtml+css zipped to epub for anything technical. The only reader that actually renders text they way I expect, right out of the box, is Edge. Epub is for novels, not textbooks, papers, or manuals.