The latest CCD science detectors have reached a size of 100 mm on its side. For delicate experiments, one needs to minimize or eliminate uncalibratable errors introduced by the instrument. This is especially critical in the case of any mechanical or electronic variations in large detectors caused by an unanticipated thermal behavior of the device, when operated at cryogenic temperatures. G-CLEF (GMT-Consortium Large Earth Finder) is an optical band echelle spectrograph that has been selected as the first light instrument for the Giant Magellan Telescope (GMT). As part of the Preliminary Design, we have developed a Finite Difference Model (FDM) that can predict the temperature profile of the CCD mounting plate. We present the model and the results we have obtained. This model is an important design tool for the optimization of the position for cold straps and heaters, when requirements such as temperature equalization or stability are considered.