Solar build—Where Is The Best Chassis Ground in the Front Area of Truck Bed?

I am putting an auxiliary LiFePO4 battery in the front corner of my truck bed. All of the outgoing circuits loop back to the negative busbar, then to the negative battery post through a 1/0 AWG wire. Unfortunately, the Victron 30A non-isolated DC-DC charger requires a chassis ground. I noticed the truck bed is attached to the frame with 4, 1/2” bolts. I want to use one of these bolts to attach my 2 AWG ground wire. I know this is not ideal, since there isn't direct contact to the frame. However, the bolts are beefy and the nuts are bonded to the frame. What are your thoughts and/or suggestions?

Both the solar charge controller and the inverter have small screw terminals on the cases for a separate earth-ground wire. I was originally going to use a 10 AWG wire, but then I read in the inverter manual that it should be no more than one size down from the size of the positive/negative wires. The recommended wire size for my inverter is 2 AWG, so that means the ground wire should be at least 4 AWG. For a wire that size, I am surprised that the lug post is only a size 8. What size wires did you use to ground your inverter?

 

There's a factory ground (on my 2019 TRDOR) on top of the frame rail just to the rear of the upper rear shock mount, driver's side.

 

Thanks! This location will work great for me. I’ll be using the one on the passenger side.

 

Do you have a picture of where you ended up grounding this by any chance? I'm working on the same thing right now. Thanks