we drove 700 miles to see grandparents when my baby was 4 weeks, and again just before he turned 3 months and he did great! he slept most of the time on both trips. i pumped as we drove and fed him a bottle about every 3 hours when we stopped (it was much quicker than nursing him at that age). he still travels well a 5.5 months old and i like to think it's because we did these long trips at an early age. good luck!
Our friends recently did a west coast road trip with their 11 week old, and they report that the travel was horrible. Their little guy would only tolerate about 45 minutes in the car at a time, and they ended up waiting to drive overnight (rough on them, easier on little guy).
If you can fly, I'd recommend it. Or, does the train run near you? Would take as long as driving but you can interact with the baby the whole trip.
The main problem i have with flying is the x-ray machines in the airports. I just know that the minute they tried to subject my child to that I would refuse and I would end up on a no fly list and go to jail because the alternative is a cavity search and no stranger is going to touch my son. So, unless there is some garuntee that they wont bother us, I highly doubt we are going to fly.
Do you mean the new machines? You can bypass those with a child...in fact, the security guards all three times I flew with my DC since the new machines all pointed me to the old machine. Even they didn't seem to want us in the new machine. If you mean the old kind...I have no experience with declining those.
Also, not everyone gets searched anyway--they point some folks toward the machine, but most just waltz through the plain metal detector.
If the pat down is a concern, I would weigh your and your baby's discomfort with a few minutes of a not-likely-to-happen pat down, with potentially hours of baby screaming in a car. You're the best judge of how he'd handle long car travel.