The Dec update for GWX is meant to be installed over GWX. To install it you must
a) Have a CLEAN install of SH3
b) patch up installation with 1.4 patch
c) Install GWX and then for the Dec update:
1. Be at port
2. Rollback SH3Cmd (if you're using it)
3. Disable all mods you're using
4. Put the Dec-update in the C\Program Files\Ubisoft\SH3\MODS directory
5. Enable the update with JSGME
6. Add any other mod you like
you're ready to roam the high seas again