Before you build too many more, Rich, just have a go at using the ones you've already done and check that you're happy with how practical and easy they are to use in an exhibition environment.
Either way they will need building, as if nothing else there are plenty of locos for Brent that need them. Longer term I think I need something else as it’s not really practical in the constraints of the layout. There just isn’t really enough time to do anything about it by Saturday week