All our motorhomes here in New Zealand have blinds and fly screens attached to the windows and roof vents. Makes a big difference to prevent flies and sand-flies coming into your motorhome. Most rental companies don’t have them or remove them before they start renting out the motorhome(s)
The Fly screens so not necessarily protect you from sand-flies, these little buggers need lees than a pinhead to find their way in. It will stop most of them though…