My first thought was Vermont, lots of gravel and dirt, but it’s better than 7 hrs. to central Vermont. Adirondacks as well, which is under 6 hrs away, but harder to piece together a 6 day tour that’s mostly dirt and gravel as the expanse of state owned land as Primitive or Wilderness areas tends to not allow thru routes in gravel. Yes there are gravel and dirt roads, just harder to piece together without a good bit of asphalt included. Note that there are a huge number of campgrounds in Adirondack Park run by the state. A lot in Vermont as well. If you consider the Dak’s I can further advise on where some of the gravel is.