If it's the rack I think it is you will only have one cord to plug in to the t-stat.
Each pc of flex is not separate but a continuous S shape thru the shelves.
I have to concur w/ Brad on a Helix or one similar.
Jeff at Boaphile recommends to place the probe right in the corner where the flex bends at 90 degrees and secure it w/ shipping tape. Place it where the cord for the flex exits which ever shelf that may be.