Fan location

[Small pumpkin]

I've just got to small fan for my tunnel. For on those days when it's to cold outside to have the vents open or when there's no breeze (that doesn't happen often). We've had a few cold days recently and it's proved there's not enough air circulation (when vents are closed) as lots of furry mouldy leaves were appearing. So where would you locate the fans?
Hang from crop bars or under the plants in the bed or between pots on the bench or a combination?

[Bigmallly]

Due to warm air rising, I would put the fans on the overhead bars.

[Deano's "Diggin It"]

As long as it's shifting n circulating air SP, don't think it really matters!

But in agreement with BM with the "Hot Air Rising" Theory!

[Small pumpkin]

Thank you both