"There is a way to wire us the single filament bulb unit so that it is on with markers, and flashes with turn signals. "

Thanks Bob, I'm familiar with that method -- one wire to the hot of the flashers, the other wire to the hot of the parking lamps. Only problem is that it flashes opposite the front and rear turn signals if the parking lights are on. It looks nice if your car's off and you turn your hazards on -- but the goal for me is to make the car more visible while I'm driving it! ;-)

Thanks,
Chris