Seitz windows

Hi, if one want to replace the blinds/flynet  on a Nuevo 53 plate, what size would they be On a S5 1000 x600  window, (completely missing)
Now roof one bust on me last night & thats not pleated like the side ones, but what size would the interior frame be do you take measurements from the outside edge or inner edge
Never thought finding replacement blinds for a auto sleeper would be so hard these loads on the roads

Roof vents are either 40x40 or 28x28 , most caravan dealers shops carry the spares.