Illustrator - stroke doesn't connect / brush pattern

so I'm having problems figuring out a stroke issue. Below is an image of what I am referring to.

Essentially, I want to create a brush that I can use on strokes so that no matter the shape, when I use it, I have 3 horizontal lines applied as the stroke.

At the moment, if I use the pattern brush, the outer corners are all over the place. If I use the art brush, the ends do not connect.

What can I do?