Re: Grounding an RV
Generally, the idea that one wire (whether the neutral of a an AC system or the negative of a battery system) is grounded to the frame/chassis/any exposed metal pieces.
Then if there are any exposed "hot" wires (broken insulation, an electrical component touches the case of a metal box, etc.)--an electrical connection causes high current flow and causes the upstream fuse/breaker on the "hot lead" to pop.
This also prevents somebody from touching an ungrounded metal box (toaster, electric drill, etc.) that has a short to hot and touching a metal sink/faucet/etc.) form getting a shock/electrocuted.
With ground referenced systems (like AC power into the home... You could be standing in a puddle outside and touch the trailer siding/door handle and get shocked if the the trailer chassis was not connected to the electrical safety ground (metal box energized with respect to ground).
A "floating system" like a battery or a transformer coupled AC system is not ground referenced until one of the leads is connected to earth. So--you could touch the positive OR negative lead of a battery or either output lead of a 120 VAC isolation transformer an not get shocked--In fact, this is commonly done on purpose to prevent shorts (using isolated power). But isolation is not done with normal household power.
Both ground referenced and floating systems have their advantages and disadvantages. Following convention is usually a good idea in the end as it prevents mistakes.
20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.