Inverter grounding to batt or chassis

All cross pieces running from side to side on the chassis are RIVETED to the frame rails and they are not welded::The easiest and most secure way to BRIDGE across the frame rails is at the engine -- the common denominator for a buss:: short lengths of 0 single aught wire can easily pass 500 amps without excessive voltage drop::I have installed systems up to 4,000 watts without the need to run a negative wire forward to the house batteries::A hole clearanced for a 3/8" bolt is fine:: Shine the steel frame rail bright:: Bolt the cable lug to the frame rail and DOUBLE NUT lock it::I use black RUSToLEUM bed liner paint over the completed work and it should last for thirty years or so even with road splash:: Spray the bedliner a few inches up the cable -- covering heat shrink tubing etc.

If you are afraid of corrosion of the fasteners, choose Silicon Bronze which will not corrode ever. It even beats 316 stainless steel.