Made a sample file for Blender 2.81+ which shows a easy way to make seamless textures for my Futanari CBBE SSE SOS Addon.    You can download the file here: seamless_sos_textures_sample.7z     Baking Tips:  To bake the seam texture select first the schlong and then "shift select" the body and activate "Selected to Active"  To bake the final texture just select the schlong and deactivate "Selected to Active"  its very important to have the right "