The first time I drew one of these reach balloons, I drew a circle, split it into four quadrants, drew straight lines to connect the end points, and used join polyline to make a single 2D entity. That I could apply a brush to and it would show. After I 2D subtracted extra pieces, the brush no longer showed.
So, it having been decided that I need to change the reach to 40" instead of 36", I tried drawing an arc for one corner entirely in a box, then a rectangle to fill out the rest of the box, then split the rectangle at the end points of the arc, made sure with the edit tool that the end points of the arc and the end points of the remains of the rectangle aligned, and used join polygon to make it one 2D entity. Now, if I apply a brush, it doesn't show.