Battery question

[Halon]

I just had a quick question about my battery setup. I'm going to be putting a much smaller battery in my car, and it's going to be located down where the emissions stuff was. Basically right beneath where the stock battery location is. Anyway, what I would like to know is if there are any rules about it being in any sort of secondary container. I'm going to make a little clamp setup so that it is secured down tightly, but I'm unsure if a track inspector would deny me from running if it's not also in some sort of little plastic box or whatever. It's still in the engine bay, so it's still behind the firewall, so I'd think I would be fine without any sort of secondary container, but I'm not 100% sure so that's why I ask. It's a 91 TSI.