Export to Markdown
Markdown is my preferred writing format. For writing fiction John Gruber's markdown format should more than suffice. So chapter titles would map to heading1 (#) and chapter subtitles would map to heading2 (##).
**bold**
*italic*
and such. From Markdown I will typically run the file through pandoc to generate ePub and PDf but that's because I like the command line, likely atypical for other writers.