I've only read the google books previews of Brads books, but im impressed. As a hardcore punk fan myself i wasn't as surprised as most to the connection the Brad Warner made between punk and zen. Also anybody who puts dirty toilets, and tattooed Buddhas with mohawks on the cover of his zen books gets my respect. People should also check out his blog: http://hardcorezen.blogspot.com/
As for meditation practice, just sitting is enough, every time i have a thought or a disturbance of any kind i just readjust my pose.
Yeah, usually when my mind starts to wander, it's reflected in slouching. I don't know which (if either) comes first, though.
BTW, if you're getting hung up on having a perfect cushion, let it go. You can sit zazen on the corner of a couch cushion. Seiza (http://en.wikipedia.org/wiki/Seiza) works, too, but I wouldn't unless you're already used to it.
As for meditation practice, just sitting is enough, every time i have a thought or a disturbance of any kind i just readjust my pose.