Recent experimental studies have found that fluid smectic phases of bent core liquid crystals form stable free standing fibers with extremely high slenderness ratios. In [1] a model was proposed to explain their formation based on the distinctive packing properties of bent core molecules in the SmCG phase. Here we develop this model further to include smectic energy terms so as to allow more general configurations and fields. We show that the relative size of the energy's elasticity constants can be used to determine the stability (instability) of circular fibers.