I converted a large stand-up freezer into an incubator, and did not install fans. I used it last season, and other than loosing a clutch to a two day power outage, all of the clutches hatched fine. Some people incubate at higher and lower temps, so I do not think that a degree or two from the top to the bottom of the incubator would make a difference.
BTW, grats on the eggs!!
Hope this helps.
I've found that fans don't just keep the temperature even from top to bottom, but also stir the air so you don't get hot spots sitting around the heat tape. I'd always recommend using fans in an incubator.
What are these mojavas I keep hearing so much about?