Gracie has very bad car sickness so whenever possible I try to not feed her within 3 hours of a car trip. My vet also gave dosing information for gravol (also called dramamine) for car sickness and it really helps. The dosing is 1 mg per pound, I bought the cherry flavoured children's chewables which are 15mg and they think they're a treat. It also helps to calm them down a bit so they relax in the car.
I brought Lady on an airplane when she was about 4-5 months old and I did bring training pads thinking it was too long of a time for her to go without peeing, but she ended up being just fine. Since you're driving you'll be able to stop every couple of hours so that shouldn't be a problem.
I used potty pads with Lady in my apartment for the first few months and she easily transitioned out of them once she got older and could hold it longer. I found them really helpful for in the middle of the night when she wanted to pee. Some people say they can "mess up" potty training but I had no issues at all they just made training easier for us.
Lady (1.5 year old tricolour) & Gracie (4 year old blenheim)
"Happiness is a warm puppy" - Charles M. Schulz