We drove from Adelaide to Melbourne (about 9 hours) 2 weeks ago when I was 25 weeks. I wore loose fitting really low cut tracky daks which were great, but found the seat belt was quite uncomfortable across my belly so ended up holding it a couple of centimetres away from belly for most of the trip.

I had lots of water and packets of nibblies with me, and made an extra loo stop than we usually do. My hands and feet swelled up heaps on the return trip, but were back to normal the next morning.

Good luck!