I don't think it's safe just locking the rear, I'd be worry more about the front rather than the rear. Since your frame has track ends, it's harder to take out the rear if they don't know how to lift up the chain, whereas the front is held together by two bolts, anyone with a wrench could run away with the wheel. You've said you live in a low crime area and there are many more easier targets than your dual locks, I would just go with that set up.