I have downloaded all the road datasets from NVDB (National Road Data Base) and extracted road features categorised having a surface of "grus", ie Gravel.
These Data Sets are compiled by Län (County) and I have exported the gravel roads in three different formats, SHP, KML and GPX. By overlaying this data on top of a Base Map it's easy to distinguish between paved roads and gravel roads. With the right Base Maps it's also easy to figure out if there are any trails that could link up Gravel Sections that would otherwise end up in dead ends.
On this page I will not go into detail as how these formats are constructed or how you are supposed to use them. My reasoning is that if you have found this link and botherd to read all this you might actually know what GIS data is all about :)
You will also find base maps that work well with the Gravel Roads, as well as links to the software and applications that I use to scout and create routes with!