Hi, Elain, and welcome! Whenever you are in a car, bus, plane for any lenght of time, you need to move around. In a car, you should stop at least every two hours, get out, walk around move your arms, hands, etc. to keep circulation going and muscles from locking up. When I'm on a bus or plane, I get up and walk up and down the aisles, too.
Be sure to read Fibro 101...the first thread on the forum. There are links to good info about fibro and you will learn a lot there. You will find a link to gentle stretching exercises that can be done sitting down and these were devised for long plane flights but can be used anywhere. These are good to do if you are the passenger in the car. Also, I have a lumbar support pillow I use to help me. Mine blows up with just 4-5 good blows. Then I can flatten it when I arrive at my destination and pop it easily in my purse! My own car has a built in lumbar support and this really helps keep you comfortable.
I'm looking forward to getting to know you better. Don't hesitate to ask questions because we are here to help you. Hope to hear more from you soon.
Sherrine