Thanks for the comment Kenya. I actually cut out the rear step sill this after noon and will be fabricating a new one to go in it's place over the next few days. I've also previously done a few repairs to the bottom for the frame so I'll find the pics of that and post them up if you like?
When you tub a Mini arch you basically raise the outside lip meaning there's more room for the wheel and tyres to travel up meaning you can run the car at a lower ride height.