I just tried to export direct from OpenOffice as html. I've got very unsatisfactory results. Text looks scrambled on Sigil and so on. I gave up.
I then used an OpenOffice extension called
"writer2xhtml", which gives more control to the user and export odt file as so-called "strict html". The results look far better.
http://extensions.services.openoffic...t/writer2xhtml
Sigil opened the file without any complaint nor showing any visible defect. I could process it easily (checking TOC, filling meta,...) and save as an epub file. But once the epub was on my PRS-505, I've got an "Error Page!" and the file can't load.
I tried many small changes to no avail.