Premiere Pro Essential Graphics - Auto-resizing animated lower third?

Hi all,

I'm trying to create a fully responsive lower third with some very basic animation on it. As you can see from the video below, it is made of two rectangles, with two layers of text on it. I've set up the animation using keyframed horizontal scales on the rectangles, and position on the text layers. Finally, a mask attached to the text layer is keyframed to follow the white rectangle back out at the end.

What I am trying to do, is to make this lower third fully responsive - I want it to expand if the name or job title is particularly long, and so I also want the intro/outro animation to adjust accordingly. Currently, the mask animation is manually keyframed - that would need to change.

I have watched PremiereGal's tutorial on this, but it doesn't cover how to expand two rectangles at once, and because the text is keyframed by position, the white rectangle would follow it across too.

Any advice or help with this would be GREATLY appreciated! Once I have made this template, it would save me and my team hours of work in the future.

Many thanks.