Problem: Cannot get any mods to work for R2.

I have taken the following steps:

1) Download mod and unzip
2) Copy the .pack file into C:\Program Files (x86)\Steam\steamapps\common\Total War Rome II\data
3) Start the game and "tick" the mod on the Steam mod manager
4) Start a new grand campaign game

Having followed this process several times with two different mods, and having had neither of them work, I can only surmise that I am missing a step somewhere.

Can someone please help with this before I lose my mind?

Thanks in advance.