For an incubator that size you should be fine with just one 11" strip down the back and one adequately powered fan at the top blowing air down. Just make sure the fan is strong enough.
How would I know if it's going to be strong enough? I thought most people just used computer fans. Do you have any recommendations?
Specializing in Ball Pythons, New Caledonian Geckos, and African Fat Tails