By default the mod cache location is set to %appdata%\SMMM
It would be a little more flexible if you could change that location so as not to lose the mods at all.
EDIT: Alright, portable has a different location, wherever the main application starts from. Apparently the portable isn't working for me for some reason. Dragging the mod has no effect. While in the installed version it works fine. I can see the mod in the list and in %appdata%\SMMM folder too.