How to Make a custom Rear Window Diffuser

    I wanted a spoiler for the rear window similar to the ones that the BMW and Mercedes guys had, but as we all know nobody makes one for the G20.  I decided to make one myself similar to the style I saw made for VW's by a company called Wet Works Garage.  It basically looks like the same thing that came factory on the BMW trunks.  I searched on ebay and I was able to get an aftermarket one for around $25 form THIS seller made for the 90-96 BMW 3 series.  This worked out to be the best spoiler for the modification.  I tried twice before to make a window spoiler, but the first one was hard plastic and was broken upon delivery and the second was cut short by me, but was not as close to the shape of the window as this one. It also comes with better double sided tape for fitting. 
    The first thing I did was clean the back window and then I took masking tape and laid it over the top corner of the window.  I cut the tape the shape as the corner of the window and peeled it off.  This created the template for this corner, I transferred this to one side of the spoiler making sure to leave enough room for cutting the other side.  Then I cut the one side of the spoiler with a jigsaw to the shape I drew on.  Now before you go cutting the other side (like I did  in my first attempt) fine tune the side you cut.  Once your satisfied with the fit, lay the spoiler on the window and tape the cut side in place tight to the molding.  With a heat gun (or a hairdryer and some time) bend the spoiler while heating to conform to the shape of the window, taping it with masking tape as you go along to hold the shape.  Once you get it all shaped, mark the end of the glass on the spoiler and remove it from the glass.  Now just like before use masking tape, create a pattern of the cut and line it up with your mark on the spoiler.  I recommend cutting it a 1/16th big and trimming it to fit perfect later, this will create a better fit and less chance of cutting it short.  
    Once it's all cut to size you need to smooth it all out and prep it to paint.  I painted mine black to match the window molding and the theme of my car, but you can paint it pink if it makes YOU happy.  When the paint is dry, apply the double side tape to the back and cut it to the new shape.  Once again clean the back window VERY thoroughly and I recommend heating it up a little if it's not a warm day.  Peel the tape from one side of the spoiler about 3 inches back and let it hang down while you fit it into the corner.  When the corner is fit right pull the tape more as you position the spoiler down the window, and as you get to the other side it should all end up where you want it.  Once again if it's not a hot day I recommend heating the spoiler and the glass a little more to ensure everything stays stuck.  Good luck

Sorry no in-progress pics