We tried a 12v car vac but there was little suction. Ended up with a Dyson mini pull along. The wand is telescopic so the whole thing fits under one of the seats. It's 240v so we've got a dust pan and brush for little jobs
We bought the little Dyson rechargeable. Not cheap but it Hoovers, sorry Dysons up dog hairs which is what we got it for. Our van has carpets everywhere. A stiff brush would do the same job I guess but hard work when it is hot.