Fitting Fridge fan advice needed

[kelv]

After just returning from Spain I have decided to fit fridge fans as my fridge was not very cold.
I fitted them on my last van and they worked great but the van I have now is a Carthago and only has one lower vent the upper vent is on the roof has any one fitted a fan in the lower vent.

 

[Figaro]

No, but I don't see why it wouldn't work the same.
Just have them blowing up to the roof.
You might need to increase the number of fans to account for the extra push needed to get the air up to the roof ?
Three fans instead of two maybe.