I'm going to start working on my car again. I want to get the electrical done. The car has a trunk mounted battery. What battery box will I need to pass tech? Car will not be in the 9's. Can I use a plastic unit or do I need a metal box?

If you have a fire wall between the interior and the trunk a battery box is not needed.

A piece of metal behind the upper seat back is all you need if you don't use a box. It must have an external master shutoff switch in the positive side of the system.
Doug

If there is no sheetmetal rear firewall, a sealed box vented to the outside is needed. The Moroso box works great. Box or not, a rear mounted battery needs to be held down by minimum of 2 3/8" studs or bolts to a framerail or framerail mounted tabs/brackets. The box or battery tray can be attached to the floor however you like. Battery hold downs need to go through to the frame.

I do both anyway, also the speaker holes according to one tech guy.
My plastic marine boxes have passed NHRA tech since 1994; they're mostly interested in 3/8" nuts/bolts & proper hold-down. Mine go through floor with large washers, hasn't been a problem.

Thanks I do have a firewall. The current battery mounts are welded into the rear cage. The car is tubbed so no rear package tray.

If it has a legit firewall, no box is required. Just proper battery retention.

This is the trunk....

I use the plastic marine style battery box. I also have metal behind my rear seat so I don't have to use a box. But since its a street car and I use the trunk a lot I don't want battery acid getting on any clothes or jackets I put in the trunk. Ron

why not use a AGM or gel type battery ?
No fluid issues . No need to use a box or vent down here if using this type of battery .

Tex

Yes I will most likely be using one of those. I have a Optima from Chumpcar... As far as I know it is still good. If not I'll buy another one.