A fuse would be just as good as a breaker here, assuming you don't need to open it manually frequently. You should have one (fuse or breaker) on each end of the line, since either battery can supply lots of current. For 2/0 cable, something around 175A or 200A would be appropriate (or lower if desired).
On my E-series based class C, Coachmen mounted this fuse on the top of the front cross-rail above the grille and under the lip of the hood. There's a little plastic shield over the works to make sure it doesn't short out. That seems like as good a place as any to me. I can post a picture tomorrow if you want.
