Omnivent - in or out to reduce heat?

Deaky

Currently sweltering in Anglesey, can't decide if it is best to have the Omnivent blowing in or sucking out to reduce the temperature in the van. The hubby says it doesn't matter, as long as the air is circulating - any thoughts anyone or other ideas to
reduce temp in the van, it's warm out there and not even 10am!