Been road hunting for many years, time honored tradition in rural Alaska where the road is closed anyway most the year but still passable with 4X4, chains & snowmachine in the bed.
Never thought much about a rest, but great idea. I just usually have the S&W 460 10 inch on the dash. I can hit caribou at 200 yards pretty consistently hanging out the window. I watched a friend hit 12 inch target at 400 yards with same gun; every other shot; but I couldn't myself.