Basically get 4 big popper fasteners from a textile shop and drill out the middle of the male one.
1. Pop rivit one into the top of the pillar above the top seat belt mount.
2. Pop rivit another on the pillar to the right of the sun visor (in the corner above the window)
3. Repeat on the other side.
4. Measure the distance between all the poppers i.e around the window from pillar to pillar.
5. Make a curtain this length, but put elastic in the hem of the window side.
6. Put the popper female ends on the curtain (sewn in or whatever) in the corresponding corners.
7. Done!
It will take you about 5 seconds to put the curtain up and wont slide around while driving. You dont need curtain ties etc. When you put the curtain up it goes behind the rear view mirror and sun shades (tight because of the elastic)
Looks well neat and you only need to drill 4 holes!
I will try and find some pics of it in place, for you