I don't think the bumps will cause harm to bubs bit might make you a bit sore if they are too rough.
I've done a long road trips in an EK holden at 32 weeks when PG with Caleb and this PG at 16 weeks so I fully understand your apprehension about lack of suspension!

The pillow might help but I think regular breaks to stretch out would be better. Lucky the petrol tanks are reasonably small