I managed to get the "forum" link in the navigation to work (that I created by making a new page and setting the template to Forum Index). I am having trouble, however getting each of the forums to show up in the subnavigation. I used custom page links to put them in the menu but it won't recognize them as current-page-item (therefore unstylable in css). I tried creating a page that displays that forum, but then I can't override the slug because it's already taken.
I suppose I could give the forum an alternative slug and only link to the dummy pages I create, but it seems like there should be a better alternative?