It is much easier to clean a dust filter than the entire box.
If this box is perfectly sealed, then having just one exhaust fan would just recycle hot air back inside. Practically useless.
If this box is not perfectly sealed, then you will have negative
air pressure inside the box which will draw dust inside.
This could help explain positive air pressure.
If you are on a budget, then a filtered, interior air intake fan and an exhaust fan would be your best option. Much less dust, not having to worry about humidity, wind etc...