I HAVE read all the posts because it annoys the snot out of me to read the same advice six times.
We road trip down to Disney about every 2-3 months from Atlanta. We've been doing this for about ten years. First car was a pickup truck with no ac and no radio. This was before kids and my husband's fondest memories were getting my undivided attention for 7 hours!
Next car was a Dodge Grand Caravan with a one and two year old. That was probably the toughest driving down since they were infants and weren't interested in a DVD. We used to leave at 7 pm and get in at 1 am, the kids would sleep the whole way.
Current (and definite fave) is a 2003 Mazda MPV minivan. It's one of the smallest minivans made but everyhting fits. It has a DVD player in it and let me tell you, it is a GODSEND. We tie the movie choices to what rides we want to see in Disney, (Dinosaur, Peter Pan, etc), and rent them from Netflix before we go. The seats for the girls are both captains chairs and can recline a bit-the graco booster seats had head support and also reclined-we're talking reclining just enough so their heads didn't loll forward and choke them.
We've tried leaving at 4 am, 12 noon 7 pm, and the evening drives are always the best, cooler, less crowded, easier to see the dvd, kids more likely to fall asleep.
Another tip, don't have fruit juice in the car, just carry bottled water. The fruit juice jazzes the kids up (not good in the confined space) and your car ends up sticky and smelly at the end. We do popcorn (not sugary, easy to clean) and bottled water.
We've never used a trunk container, so I can't comment on whether they'd be good, but the less junk you take down, the less junk you have to take back. We still fill every bit of space in that car-the rear seats tumble down into the floor and all our stuff just gets shoved in.
We also use dark colored fabric to tie up along the girls windows and the rear windows-it doesnt affect our vision, but it cuts out almost all the light of the florida sun and makes it easier for them to sleep-I have little velcro ties on the top and just wrap them around the hand grabs above the doors.
Be careful where you stay in Savannah, some parts are pretty skeevy. And it's pretty expensive. You might want to find a nice place to stay far outside of Savannah, unless you want to stop and do touristy stuff.
Road Tripping Can Be Fun!