WINCHESTER BAY — Gary Leif can’t get enough of riding the dunes. The Roseburg resident and his family have traveled to the Douglas County coast to drive off-road vehicles in the Oregon Dunes National Recreation Area for 35 years. Leif and his wife, Carol, now bring their grandchildren riding, but he worries a Forest Service plan that would limit off-road use on the dunes means their future trips won’t be the same. Leif is among the Douglas County dune riding enthusiasts revved up over the Forest Service’s plan to close off-road vehicle trails through wooded areas on the dunes to …