FSR's.
One for the lead, one for the sweep and one every 8-10 cars, preferably cars with passengers and people who really know each other that way your max range only has to bee a hundred yards or so and you can relay info down the line.
Most important is to forget about an organized run, you give a destination and tell folks here are the ways to get there but keep up and follow the leader is the most fun, if you are insistent at keeping a group together then you need corner markers, cars up front who will sit and wait until the previous 'sweep' goes by and make sure everyone got turned in the right direction and then takes up the sweep but that takes serious planning and work and frankly who needs that.
