San Tsu has created a wonderful program for auto-installing custom Sins maps. You can find the thread about it here, in the Modding forum:
https://forums.sinsofasolarempire.com/322124/#1852978
This program takes Sins map files that are packed with the auto-installer program (.snmp files) and it automatically installs them into your Sins game. It automatically moves the .galaxy files (map files) into the Galaxy folder and the .tga files (texture, title files) into the Textures folder. Note that it might first be necessary to unzip a .zip file in order to get to the .snmp file.
