Rather than using a `Rectangle`, consider a [`Pane`](http://reference.wolfram.com/mathematica/ref/Pane.html) that is `Framed`

    text = "Bunch of random text ";

    Framed@Pane[StringJoin @@ Table[text, {10}], 300]

![enter image description here][1]

The second argument to `Pane` determines the width in points.

If you want more control over the text within the `Pane`, consider putting a `TextCell` inside the `Pane`. If you just use a `TextCell`, you can't control its width.

    Framed@Pane[TextCell[StringJoin @@ Table[text, {10}], 13, 
      TextJustification -> 0], 300]

![enter image description here][2]

I appreciate that my proposed solution isn't a `Graphics` object, but it gives you the desired result. The question is whether you need this in a `Graphics` object or not.


  [1]: https://i.sstatic.net/QhKIP.png
  [2]: https://i.sstatic.net/SEwas.png