With one car done - a kind of proof-of-concept - I set about doing a couple more. These look a bit 1970s to me.
Although in a game they'll probably be armed with anything the system throws up, I went with rocket launchers for one and a couple of missiles for the other.
I decided on yellow and green for the colours.
The finished product. I'm tempted to put some marking or artwork on them to break up the block of colour a little, but I'm not sure about that yet.
The green car has an odd door, obviously fitted to replace earlier damage.
Update: A thin black wash into the gaps of the doors, bonnet, boot and other bodywork really helped to break up the colour. Strangely a light dry-brush of brass on the rusted metalwork also helped improve its look as well.