Tenba and LowePro make rolling cases with the twelve inch internal width required for the M Line Two. I use a Tenba Universal, the smaller of two large rolling cases, which also fits nicely in the overhead bins of most airplanes (except for some very small regional jets).
After three years of moderate use, the top handle of the Tenba is getting a bit loose, but otherwise the case has held up rather well.
David Kaufman