I don't have much experience with incubators but my mini fridge bator looks to be about the same size as your red bull fridge here. I used 3 feet of 11inch flexx watt. It might be a little to much but it is more efficient in the long run, the flexx watt is barely running to keep the bator pegged at 89.
You might be able to get to your desired temp with enough 3inch but in my experience the 11 inch would be the way to go.
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