On my Navara the brake power also comes direct from the battery through a 40A thermal breaker. Cables pass in through the firewall, back out through the firewall and down under the cabin. Typical claim by the auto electrician that did the job "4mm cable is more than enough" but I insisted on 6mm "overkill but ok we'll do it". Given the costs involved going to 8mm cable wouldn't have been much more.
Watch the grounds. They grounded mine on the installed hitch and I had to change that. Now I have 4 8mm cables running to the rear (2x positive and 2x negative). One is connected to the tub and my trailing Anderson plug and the other directly to the trailer plug (with the earth replaced). Guarantees not only a good connection but a good flow of power.
As far as legislation goes, we need to tread carefully. Slowly, all of the states are coming into line with the same legislation following the national code. It makes sense, but getting the state governments to pull their stupid heads out of their skanky butts isn't easy to do. However, they're all pretty much going to go down this path: if brakes are fitted, they must work. Insurers LOVE when they don't, because that places the onus of failure on the owner of the brakes. They get to pay out to their client (minus excess which is a payday bonus for the insurance execs) and dip into your pocket for all costs + legals + whatever else they can put their snotty fingers to.
They're actually the bigger worry. You can drive around at a couple of km/h below the speed limit, indicating properly and obeying all the rules, with a 4T caravan sitting behind a 3.5T D22 and the cops won't touch you. Why would they? Their job is to target obvious offenders. Don't worry about the cops. Worry about the idiot who careens through a give way sign into the side of your rig. Yes, you were following the obvious traffic rules, but as soon as your vehicle breaches a technical requirement, it is unroadworthy and therefore should not be on the road. If it shouldn't be on the road, then the idiot that hits you isn't actually liable - YOU are.
Messy, messed up and not even morally on the right side when that can happen, but I used to work for a law firm that worked on the insurer's side, and have seen the results when the lawyers came back in after a hearing and winning it (and 10s of thousands in costs awarded) on a technicality. Drinks all 'round.
And the poor bugger who failed to meet the technicality paid for it all.