Good to know and thanks for the recommendations!The route from DC to Michigan via turnpike is totally viable - we've done it dozens of times. You'll need to exit the turnpikes occasionally to hit a Supercharger, but the diversions are typically very short.
Currently, the biggest stretch between turnpike Superchargers is Somerset, PA to Genoa, OH at 277 miles. That's a bit of a stretch for a 3 or a Y in all but ideal conditions, so a quick hop off the turnpike for a charge at the Sheetz in Strongsville, OH splits the gap quite nicely.
It's seriously no sweat at all, even in crap weather. Just set your destination in the navigation and let the car plot your course. Make adjustments if you need to - there are several alternate charging options along the way.
My recommended route would be Frederick, MD to North Huntingdon, PA Supercharger (immediately off the PA Turnpike, 176 miles); charge enough to reach Strongsville, OH (short diversion from the Ohio Turnpike, 150 miles); charge enough to reach Genoa, Ohio (Ohio Turnpike, 91 miles);t hen charge enough to arrive at your destination with a comfortable buffer, or enough to reach whatever Supercharger you need in Michigan.