From downtown Rapid City take hwy 16 south for about 25 miles to its intersection with hwy 385, turn left and the Naked Winery is about 1 mile on your left. The winery is about 3 miles outside of Hill City. There is no oversize parking lot at the winery (unless its empty and they let you park out front along the hiway entrance). But between the winery & the lumber mill there is a large dirt parking area, about a block away. Not sure who owns that property, it may be overflow parking for the lumber mill.
As with most tourist towns, parking within Hill City itself is limited. Best to park the rig in your campground and use the towed for local touring.
Jim