I have driven it many times. From Baltimore it's exactly 900 miles, but the route is very simple - I-95 to Tampa, then I-4 to WDW. Couldn't be easier! We have never rented; we always use the biggest vehicle we have, which is usually a Chevy Astro (very comfy). Once we used a Honda Passport, which was okay but not as comfy as the Astros.
Change your oil before you leave, even if you are not near the regular time, and have all your fluids topped off and your A/C refrigerant checked. It's also a good idea to put fresh refills onto your windshield wipers, check tire pressure (DON'T FORGET THE SPARE!), and make sure you have an emergency road kit with flares, jack, tire iron, etc. A little preventative maintenance can stop potential probles before they even happen!
Get the car's interior cleaned just before the trip, it makes it more comfy than riding down in a dirty car. Go easy on scented cleaners and air fresheners, though; you will be stuck breathing that stuff for 14-16 hours!
It takes about 14-15 hours from Baltimore. I have always driven it with at least one friend who can drive, and we switch off every 3-4 hours. Boredom is the worst enemy on a drive that long - both for the driver and the passengers. Whoever rides shotgun is the navigator, and has the responsibility of keeping the driver alert. If you have more than two drivers, mui bueno, because then somebody can take a nap. If you only have two drivers, the navigator should nap at the beginning of the other person's shift, not the end.
Pack a variety of snacks and drinks. Don't just pack a big bag of chips and be done with it - after about 500 miles, those chips start to taste like cardboard. Pack at least 3 different types of snack (chips & pretzels, some sweets, some veggies), and pack some sandwiches for lunch and dinner. Keep some of this stuff in a small cooler within easy reach. And don't forget some plain old water - there are times when plain cold water tastes better than any soft drink, and you can also use it for cleanups.
Keep a roll or two of paper towels, some wet wipes, and a bottle of spray cleaner on hand. A whisk broom might also be handy. Stuff happens - food and drinks can spill.
Make a restroom stop at each and every gasoline stop.
Keep your camera handy in case of pretty scenery.
Sunglasses on a cord are much easier to take off and put on as the sun moves across the sky. They also don't get lost as easily.
If you are leaving during cold or rainy weather, get the car started 10-15 minutes ahead of time to make if warm and cozy before you get in. Then you can stash your jackets in the back instead of sitting on them the whole way. If ou are leaving in hot weather, start the car early and get the A/C running; you might also put a few towels on the seats to prevent sun-heated seats from burning your legs - these will come in handy in Orlando, too.
Make sure you have highway maps of each state you will pass through, and find a good map of Orlando, and pack these up front so the navigator can easily reach them.
Keep drivers license, insurance card, and registration in a handy spot in case of accident or cop encounters.
Keep track of your position constantly; this helps to keep you awake and alert, and makes the time go a little faster as you pass major crossroads, towns, and landmarks.
And relax! You will be in the car a long time, enjoy the scenery and each other's company.
