NHRA rules

If you put the battery in the trunk, Yes, you need an exterior mounted On/Off Lever and/or switch that is clearly marked On/Off. It's for safety, if ya happen to get into trouble the 1st thing they'll do is flip that switch. It also needs to kill the engine aka flip off engine shuts off.

I'm pretty sure you only need a rear firewall if you have a fuel cell inside the trunk area.

I'd reccomend one of the Optima Batteries, I'm pretty sure they'll pass tech with a basic battery box, securely mounted.

Pretty much mysetup Optima Battery in non sealed box, Switch located 3" left of right tailight.

You didnt mention WHY you wanted to do this. As a generalization If you need traction on the right rear or are running faster than 11 sec It's a good idea.

Hope it helps, Eric