Hello Ian
Are you still enjoying the french hospitality?
The choice of fitting and style of windows is usually left up to the individual builder as there is such a wide range of preferences.
The easy way is to tidy up the edges of the window cutouts and stick a piece of clear plastic or acetate on the inside, alternatively you might want to improve the design by including window frames [in either timber or metal] or even go to the extent of having opening windows.
I opt for the easy method and apply a thin coating of fine wood-filler to the open (cut edges) of the ply before tidying up with fine grit paper, this seals the ply and produces a nice flat surface with crisp square edges prior to painting.
I hope this helps but if I can be of more assistance please don't hesitate to ask.
All the best
Paul