I've tried both the offline installers and through Galaxy. Anyone else having this issue? The DLC should just appear in campaigns, shouldn't it? The base game works fine.

I'm guessing that it managed to route itself into a separate folder, rather than the main install directory.

Figured it out, but thank you anyway. The game doesn't load the DLC by default. Here is how I did it, if anyone else searches for this problem:

install game and all dlc, start game and click on the numbers at the top right of the main menu. a box will pop up on the desktop. click install, go to folder of game, click on the .gt3ext files.