Hopefully, this can be answered by a simple yes or no.
I understand the wording on: the bottom of the chassis cannot be bowed.
The question is: If I insert the steel rail into a brass tube (round or square) to aid in soldering, technically, the bottom is no longer flat. It's flat as opposed to sagging in the middle, but it's also stepped.
Did I explain that clearly and concisely? A little more to it than explaining that the earth is flat.