[zalew]

> Why not go further and put up the train carriage specs/dimensions in an easy to use template online, so you can lay out your design in advance to take account of the windows.

such stuff has been available in graffiti shops for decades :) but a little hint: nobody cares about windows :)

> Going any further like sponsoring chosen designs might backfire because then it all gets viewed as too commercial, and we'll get people defacing the corporate graffiti.

yes. google for 'adisux', an Adidas' Warsaw fiasco when they covered part of the horse racing track wall (longest graffiti gallery in Europe) for an ad and got trashed to the point the scandal got to tv, their pr firm got into panic mode for a week and in general, how to say it, their marketing campaign didn't work out.