No, power from the 7 pin is useless... it is disconnected. I have a 30A DC-DC charger with 6 AWG wire from the truck. It only allows power to go one direction and charge my bank when driving.Is it also fed from your vehicle 7-pin?
That’s the start of issue
Do what works for you if you deem it safe
I prefer separate brake systems when we put high power batteries and SCCs into our RVs