Looking to build a one clutch cooler incubator

Hey everyone! Man it's been a while since I've been in here, school has kept me busy!

Anyways, this season I'm going it breed my normal female to my super pastel het pied male, it's not my ideal clutch, dealing with possible hets, but I want a clutch of eggs under my belt before I have 5 clutches next season.

Looking to build a one clutch styrofoam cooler and I have a question, is a fan necessary? I've seen people have water bottles lying on top of the heat tape, does this eliminate the need for a fan? Or the cooler being so small a fan isn't necessary?

Any opinions would be great.
I'm so excited!