I always build my own and include a security/safety device called a latching solenoid. The latching solenoid enables me to completely cut (or restore) power from the battery with a single push of a hidden switch. You can't hot wire the car without battery power.

I use 1/0 cable and hide the latching solenoid deep so getting to it takes work and figuring out where it is.

I've used a simple grounding device right at the battery and a firewall bulkhead to transfer power into the engine compartment and provide power taps on both sides.

The engine to firewall ground strap needs to be heavy to carry the starter current.

I've used this setup on three Mopars with 10 years of reliability and zero failures. I noticed Painless has picked up on the idea and sells a very expensive version. Make sure you use the Cole-Hersee version solenoid if you build your own.

Latching Solenoid