Grounding an Inverter?

Flapper wrote:
Sorry if this is silly, but I'm not that familiar with conventions of doing electrical work on a vehicle that uses the chassis as the negative conductive path.
So, I'm installing an inverter in my 5th wheel. Directions say to run pos and neg wires to the inverter from the battery (2 wires makes sense, given the current they might be handling). Then they say to run a ground wire from the inverter ground connection to the chassis of the vehicle. Now it just so happens that the only negative lead for the battery grounds to the frame. So, electrically, rather than ground the inverter to the frame, could I either a) connect the ground wire to the negative terminal of the battery, or b) just tap off of the main neg. going to the inverter, and use the tap to go to the inverters ground?
On the 120v side, it has a GFCI outlet - would either of the variations above mess with how that works?

Internal to the inverter the battery negative connect, also chassis ground, is often NOT carried over, connected to the inverter output side. GFI may not (cannot?) work unless the inverter case is connected to the RV chassis ground.

ALL 120 VAC current, amps, flowing in the HOT side (black wire) of the 120 VAC source MUST return on the neutral (white) wire. If ANY current is detected flowing in the 120 VAC ground return (green) wire the GFI will trip, open the circuit.