Wiring 4 awg charging wire to upgrade 8 awg factory wire.

Thanks. I will check out the NAPA connectors That premade cable is way too expensive! I was originally looking for an Anderson connector and chassis mount receptacle but have not been able to find one yet that will take 4 awg cable. Will keep looking.

But am I right about where to connect? At the current ACR battery terminal?

Go with an Anderson connector, minimum of 100A though the cost is about the same for a 175A connector. Upgrade to 2 awg and use welding cable as it will be flexible yet resistant to uv and oil. Find a place you can drill one or two holes through the camper exterior to where you want the truck side plug. Let the camper side just dangle with enough slack to where every you plan on solid mounting the truck side. Since my battery is in the back of my Lance 815, I mounted the truck side in my rear bumper and the camper side goes from the battery right out by the tail light. You will want the battery cable to go to a breaker than to the DC-DC charger which will then get hooked up to the battery.

Napa also has a premade cord as well, but I think its way too big for your needs.

https://www.napaonline.com/en/p/PHI232326

Napa has a 100 amp 2 wire Lift Gate Plug set you can use to add a heavy gauge umbilical between you camper and your truck.

https://www.napaonline.com/en/p/PHI15326 - Outlet
https://www.napaonline.com/en/p/PHI15336 - Male Plug

There has to be a line side wire on the ACR as well. Thats 8ga and 4ga coming out on the load side?
Either way, you’d want to hook into the line side of the ACR, unless maybe there is a disconnect ahead of the wire going into the ACR.