As a small-time competitor, this is my view:

I've built a new, very solid and compact bot to the current rules which has cost me a lot of time, money and effort to the current rules. I understood that there would a some rule that along the lines of a 2mm+ metal plate beneath the lipo so that's what I've done. The base and removable lid are 3mm steel and the lipo is secured between these and two motors cases which in turn are connected to one mount (there is also foam in there for shock protection). This is the best standard of mounting I've used and all my past methods have passed tech check.

Now, just over two weeks from the start of the season, the rules will probably change. There was no warning that this rule would be stated the way it has been and if its going to be a rule that the lipo has to be in metal box, I can't see how this is fair on people who have been working over the winter to a current rule set? I, for one, won't be able to fit such a box around my current battery which would fit in my bot (unless I use tin foil, but again, that is metal!) so that would be a hell of a lot of money down the drain and I'm not too sure whether I'd be willing to take that.