With the current "Auras not showing in config screen" bug that many people have, including myself, it's hard to get any help like this. I would be able to help were the auras showing up in config. Sorry.
If you can't get WeakAuras to work properly due to whatever bugs are going on, there is an addon called TotemTimers that has a bar that fills and changes color as you build MSW stacks (goes from empty to red, to yellow, to green when at 5). Now this addon does have a bunch of other components to it, but they can all be turned off. You'll also need to disable some of the visible buttons if you just want the MSW bar visible. Just wanted to offer another option if WeakAuras aren't working (as an enh I also love TotemTimers).