The Cross NH Adventure trail starting from Airport Road in Whitefield to the North Road in Shelburne is one to consider. It runs through a Fish and Wildlife refuge and the WMNF. No official campsites but plenty of places to camp. Unlike most of the rail trails in NH and VT, this section is just the old ballast and a lot rougher than a typical rail trail so its easier walking and far less traffic. There are local shuttlers. Hard to beat the views as it follows the Israel RIver and Moose RIver drainages. There is one short section shared with ATVs in Gorham that can be dusty but there are ways to bypass by walking local roads.
Cant beat the views in this section
https://www.xnhat.org/