You asked a question - you got an answer that quotes the manufacturer. Without giving any more details about your attic or climate, what more do you expect? We certainly don't know where you live or that your attic has spray foam.
If your attic will never get over about 85° it'd probably be fine - but if it's going to get any warmer than that or have big changes in humidity, just don't do it. If this is new construction, you can put it anywhere and a flush-mount box between studs literally takes up zero space - it'd be smarter to pick a better central location for not just the Elk, but all your structured wiring components as well.