I can't see the photos but I generally recommend only one fan. When I built my Red Bull incubator I only put one fan (although it was a bit larger than normal) and I had a problem where my incubator was holding heat too well and the little bit of heat produced by the fan was raising the temp up, even when the thermostat was not applying heat.

So that is my 2 cents. If you go with 2 fans just be sure they do not generate too much heat.