So having decided I want wrecks rather than cars, the first step is to take them apart. This is not too difficult, partly because they are made of very poor quality plastic - then again what do you expect for 9p each including shipping half way around the world?
I found it reasonably easy to pry the chassis part from the main shell, then punch out the clear glazing bit (and bin it as not needed). The people carrier was the worse to do, and I did end up damaging some but that shouldn't be an issue thinking about the end result.
Once separated I quickly and roughly painted the inside of the bodywork on the brighter coloured ones black \ grey as I don't want the bright colours showing through and painting them later will be a pain.
Next step will be to stick the shells back to the chassis then start thinking about rusty and wrecks