After having similar frustrations, I came across the wp-unformatted plugin. Basically you just add the key/value pair ‘sponge’=1 to any post, and the editor will not mess with the raw HTML. The downside (and not obvious from the documentation) is that you have to put all the <p> tags in the post yourself.
Can I please get some help on this? Does anyone know what I might be doing wrong?