Inverter Chassis Ground on Copper Propane Line?

Great info. It sounds like I need to find the frame ground. I think I remember seeing a picture of grounding straps that attach to my truck camper's tie-down points. If I can get to one of those straps, would that be satisfactory? I guess I traced the wrong wire and/or was assuming the panel was grounded to the tubing. There must be another ground wire I didn't see.
Thanks for the info. I'm glad I asked. I know just enough to be dangerous. Any other input is welcome.