MB4 215a: Flimsy Walls (360:1-3 - part 2)

A makeshift wall of vertical-only or horizontal-only posts with less than 3 tefachim in between is valid for an eruv (lavud) but MiDrabbanan it can't be larger than בית סאתיים. Regular walls permit carrying in an area larger than a בית סאתיים.

If there are three adults then they can qualify as a שיירא and carry in an area larger than בית סאתיים even with flimsy walls.

The rules for three people in a caravan making adjoining eruvin.