As of version 1.14, wget natively supports warc (including built-in gzip and cdx index file generation).

http://www.archiveteam.org/index.php?title=Wget_with_WARC_ou...

This makes creating a browse-able mirror of a site in warc format fairly straightforward, as wget will automatically make links relative, as well as fetch requisite files (css, js, images) for each page.