Really easy DIY. As long as you're careful, you do not need to replace the clips or seals, so don't waste any money on a fitting kit. The instructions are in this link: http://www.z4-forum.com/forum/viewtopic.php?f=28&t=1568
I did mine in about 30 minutes for the first side, and perhaps 10 for the second....
.....oh, and since us vultures seem to be a-flocking, let me know what price you have in mind for the back boxes if Markos changes his mind