At least one Fat Uncle used by Zeon Remnants was moderately upgraded, with extensive modifications made to its chassis. The engines were moved from the sides to its dorsal hull, and large sliding doors were added to the sides of its main body. Its armament was downsized as well, with its three twin machine guns replaced by a pair of smaller single machine guns. These changes granted the Fat Uncle much greater speed and mobility, as well as a higher flight ceiling - allowing it to fly higher for longer periods of time.
In UC 0096, the Zeon Remnants made use of at least one Fat Uncle Custom during an attack on Torrington Base. This aircraft carried Yonem Kirks's MS-05L Zaku I Sniper Type high above the battlefield, allowing the mobile suit to fire down on enemy ground defenses from a safe distance. The Fat Uncle Custom would later be shot down by RGM-96X Jestas used by the Tri-Stars Team.