"Thinking about grounds, if we're looking at voltage and current between the converter and the battery, aren't those the only two grounds that would matter in that calculation?"
Depends on the set-up in that rig. The neg path from converter to battery via the frame can include the grounding of the converter inside the power centre with their metal chassis touching and the converter sharing the big 120v bare copper wire from the power centre 120v intake (shore) cord to the frame plus maybe having its own wire to the frame. Might be a shore/gen transfer switch amongst that. Behind the converter there might be a whole bunch of white wires wire-nutted together with the converter's mixed in with them.
At the battery you might have a Trimetric monitor shunt which means the battery ground to frame is on the other side of the shunt from the battery post neg connection to the shunt. You might have a battery disconnect on the neg side near the battery too.
Could be more variations, especially in a MH, which are complicated compared with trailers. As a trailer owner, I find MH electric set-ups just baffling :)
