Patricia, for PG books libprs500's HTML2LRF utility works great, it formats better than "Book Designer" as it supports the CSS formatting used by PG HTML books. It's very easy to install and use, and you don't need to edit anything.
Have a look
here
All you actually need to do is:
* Install Windows package from
https://libprs500.kovidgoyal.net/wiki
* Get your HTML zip file from Gutenberg and extract it, e.g.
http://www.gutenberg.org/files/19420/19420-h.zip
* Then run "html2lrf" on the .htm file in a command prompt.
* Copy the LRF file to your Sony Reader.
* Done
I've written a wrapper program to do all this (works with libprs500) as well called "gutlrf.pl"
here
Using this program all you need to do is enter "gutlrf.pl 19420" at the command prompt and it does everything (downloading, extracting, adding page breaks etc) for you automatically producing a nicely named LRF file that you simply copy to your Sony Reader.