For those who want flexibility from their Bear Sentry.

Expansion Packs can increase your Base Camp perimeter. The Bear Sentry energizer can support up to 20 km of wire so almost any sized enclosure is possible.

One pack lets you install a door without sacrificing area (ie you wouldn’t have to use 2 of the 6 posts from the basic model

You can add a line to the 3 that you are able to string on the basic model. The posts can support 5 lines.

Expansion Packs can also convert a Backcountry model into a Base Camp (a  feature).