Thanks GarySS,

I used a 0,5 mm (0,02 inch) thick clear PETG plastic to all windows, the method I used is the very same Sig recommends when making a genuine J3 out of their kit. So, it was very easy indeed. I didn´t use the J3 kit´s balsa blocks in upper corners of the windshield, I just glued the plastic in place without those blocks, using only 1/4 inch thick hard balsa pieces which follow the wing LE profile exactly. PETG is a bit easier to bend than the original Sig window material, that´s why there was no need for vacuum forming etc.