I haven't made any windows yet, the main reason is that it shouldn't look like a camper. It is easier to park it at regattas if it looks like a box for sails and equipment and not a camper.
There are four air inlets at floor height and two ventilators in the roof to get the air out, one of the ventilators has a fan the other one uses the air flow outside the cabin to get the air moving.
I have a roof hatch as escape hatch and that one provide good ventilation when it is opened.
/hakan