Here's a different thought: you could paste these blog posts into Word and clean them up there, using a simple Normal style (say 12 point Times New Roman, single spaced, no indents in paragraph, no space between paragraphs, justified text). Save as a *.doc file (I've never really gotten into *.docx) and run it through Word2CleanHtml.com online. (Or use Toxaris's plug-in.)
Then open the html in Sigil and find a basic style sheet somewhere. (Mine is on my blog at
http://notjohnkdp.blogspot.com/ and you're welcome to borrow or adapt it.) Then tweak it to your heart's content, frequently using the Flight Crew validator (now a plug-in).