Thanks John.
I haven't had an issue with stability. Admittedly if I were to build another one I would change a few things like the mounting points, but I've been cutting, welding, grinding, had to use the cold chisel occasionally for stuborn spot welds and scraping off paint and underbody sealer without problems. If you push hard enough on it, then obvioulsy it can start to roll a bit, but in spite of it being a totally bare shell, there's still a enough weight in it to keep it steady.
The only thing I won't do is climb inside the shell while it's not supported, or get underneath it for safety reasons. But really, I don't need to do that anyway because I can just tilt it onto it's side.
