Ramslade storage facility, fly infestation

What a nuisance for you, and I think it could happen anywhere.  We sometimes find them starting to gather in our window frames at home (ill-fitting wooden frames).  We have also experienced it when opening up a house that had been empty for several months.  

I can suggest buying gel air-fresheners, you might be able to find one that is a fly killer too.  This should deter them from choosing your van.

They are not a 'dirty' fly like bluebottles.

Good luck

Thank you for the advice as it was challenge.  They appear to be getting in throgh the fridge / cooker vents in the main.  We will take your advice and place the gel repelants to deter them. 

I aghree this is a risk anywhere and moving to another storage site might not be the answer.

Not sure what sort of fridge you have but covers for most makes vents are available quite cheaply from most dealers.