I always loved car trips (I am crazy, yes) but when we had our now 5-year-old, we had to cut down on them ALOT. She hated the car seat and cried each second in it.
So, what we did was break down our usual 12-hour car trip. Instead of driving 12 hours with two short break for meals, we made it a two day trip. We would check into a Comfort Inn (they are cheap and usually have brand new room cz I hate old smelly hotels). We would drvie at night when she was asleep. I learned to nurse her in the car in her car seat (THANK YOU LA LECHE LEAGUE!). 5 years later, she loves car trips like we do. She loves arriving at the hotel and Mommy throws her on the bed and she jumps around and we cuddle. Then we swim in the hotel pool and (lately) work out together.
Take familiar things from your house. For example, her bath toys go EVERYWHERE with us. So when she arrives at Grandma's or at a hotel, she still has Mouse Girl and Mouse Boy and their car, rubber duckies, North and South, her familiar soap, etc. There is a little bit of home in the car and when we get there. As soon as she was old enough, she had her own suitcase, and as much as I wanted to pack her clothes in there and not cram them in with mine, I let her pack whatever she wanted. The other day, I was in a hurry and I was saying How about this? How about that? Mommy, this is my suitcase, I decide what I am taking. Oops, you're right.
Of course, we still don't take as many as we would without her, because it is MUCH harder traveling with children. But as long as you accomodate their needs, stop when they need to stop, rest when they want to, etc., you should be OK. Allow yourself alot of time. Last month, I drove to a city that was only 3.5 hours away, and it took us 5 hours.
Good luck. I think Mothering magazine had an article about this not too long ago. Does anybody remember it?