Personally, I would not take such a large rig through Liberty Road. That said, U.S. 61, a.k.a., "The Great River Road," a.k.a., "Blues Highway," is four-laned from I-110 in Baton Rouge to Natchez. Perhaps not AS scenic, but certainly imbued with history as there are many 18th & 19th century homes preserved along the route.
The Trace, OTOH, does
have height restrictions (14' according to NPS.gov - http://www.nps.gov/natr/planyourvisit/rvs.htm
) and a 50 MPH speed limit; slower in some areas. The NPS does stress that The Trace is also bicycle-friendly and emphasizes that cyclists share the road with everyone. This may not be an issue as it is not yet Spring/Summer.
I also save my "Natchez Trip" for the fall to enjoy the "Great Mississippi River Balloon Race." But that's just me.
John E. Baker, III and Sally Baker... The Traveling Siblings! — Watch your tail swing... Keep the greasy side down and keep it 'tweeeeeeeeen the ditches, Y'all!