I did mine myself, had to have 2 attempts that failed before I am happy now with the third. I used cheap foil from a halfords-like store here in germany and each roll was about 7 quid, so no real damage. I absolutely wanted to keep the rear window foil in one peace, which was why I needed 3 attempts.
Went about it like so:
- cut foil roughly to measure
- wet the outside of the window
- put foil on the wet window with glue side facing you, do NOT remove glue cover sheet.
- cut foil to exact size
- use hot air gun for at least an hour to bend the foil according to the window. I found that a hairdryer is not hot enough so I used the hot air gun.
- wet inside of the window
- lift foil off outside and remove glue cover sheet, best use a second pair of hands.
- put foil onto inside, align it
- use hot air gun again and again and again....until you have all bubbles and crinkles removed, might tale another hour.
ready. easy....

And I am very satisfied with the result, see for yourself:

It is not perfect, a few tiny bubbles have still survived, but they are hardly visible . Bearing in mind that I would have had to pay 200 quid somewhere else and now only invested 21 quid I can live with that. Still thinking of tinting the rear door windows but I am not sure if I can mannage them because of those big black rubber window borders...time will tell.