Well after searching the house for metal tube to use as a cutter, or anything as a template, I decided to create the window shapes on the PC and print them onto Tamiya tape.
Put the tape on a piece of glass, then with a new scalpel blade in the handle, away we go. The glass is only a small piece so it can be turned while cutting around the curves.
The Tamiya tape is the wide stuff, 40mm, and its different stuff to the narrow stuff, seems thinner and has the name 'Kamoi Tape' in the centre of the roll.
Here are the cockpit windows masked..
I've masked the rear with a larger piece of tape than the outside of the windows, hopefully we don't get the double pane look.
I am feeling happier now.