It's just whatever you want. I used a RoadRunner hardcase when I used a rack amp. Anything that fits, will work, and you don't "hafta" put it in a case, if you don't want to.
I am really happy with this Gator rack as it is super light, has full front and back covers, is solid and strong and makes my M9 very portable and easy to carry around. It was cheap too! Being this light, compact and strong makes this a much better option then a soft rack bag in my humble opinion.
And there's room for a tuner!
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Dwelling on the banks of the deep end.