I've been trying some stuff. After getting the Black Beauty TXT from Gutenberg, I made it into a default LaTeX article, stripping out all Gutenberg stuff, without changing anything in the markup apart from denoting \sections and \subsections to create the ToC. (Even the page number on the title page is still there.)
Then I output a PDF using pdflatex, which can be downloaded here:
http://www.silverforest.net/f-i/mobileread/beauty.pdf
After that, I output an HTML file using htlatex, which can be read here:
http://www.silverforest.net/f-i/mobileread/beauty.html
And at last, I tried to create the epub file using PanDoc, first starting out with the LaTeX file, and then with the HTML file. The LaTeX->epub conversion worked, but it was quite bad, loosing the table of contents, and ignoring sections/subsections. HTML->epub created quite a good epub, but it basically was an "epub"-ified version of the HTML, which is of course logical.
Many things such as page breaks need to be marked up after the HTML->epub conversion, where LaTeX can do that by default; seeing that I still have to do work after the conversion, it is easier to start out with the textfile in Sigil; the only difference is that this time section/subsection (chapters) will be marked in Sigil, instead of LaTex.
If I need a simple, well-readable PDF or HTML file quickly, I'll use LaTeX, and I still wonder why there is no good direct LaTeX to epub convertor, seeing how very quickly a plain text file can be whipped into a well readable document.
To be honest, I woudn't know how to create an epub without Sigil, at the moment.