Coding of civimail header body and footer - best practice
I've been using something like this by adding HTML to the CiviMail Header and Footer options. 


https://gist.github.com/danaskallman/57616e7d17cc4c4f5050
https://gist.github.com/danaskallman/1a40f03900a631c6389b


It works nicely, wraps around the content area so that no HTML has to go in that area if not wanted to do so. Works best with Single column newsletters, which I believe work best on mobile anyway.