Power protection with generator

If you want to use power protection, the smart ones might not let power flow since the generators have a floating ground. In that case, you would need to purchase or make (really simple) a bonding plug to tie together the neutral and ground terminals. Then the circuit analyzer will be happy and let the current flow.

Bonding plug:  Take one 15A male plug sold at the hardware store for repairing extension cords. One meant for outdoor use is probably best for this. Open the plug and locate the neutral and ground terminals (usually, hot is brass color, neutral is silver color, and ground is green). Take a short piece of 10 or 12 gauge wire and connect the neutral (silver) terminal and the ground (green) terminal. Do NOT connect anything to the hot (brass color) terminal! Close the plug and (if desired) squirt some silicone sealant in the hole through which a cord would normally run to make it water resistant.

Use of bonding plug: Plug the bonding plug into one of the 15A outlets on your generator. Plug your circuit analyzer or extension cord into one of the other outlets (15A or 30A as appropriate). Start your generator and run as normal.

RV's have no grounding system themselves, when grid connected the ground connection is provided by the connection to the RV park or home electrical system. So when you are disconnected from that and are running on a generator there is no earth ground connection. That's OK as long as everything is bonded to the trailer chassis.

The trailer electrical system (both the neutral and any metallic components) are bonded to each other and to the chassis at the power panel. So if you connect your three wire (two plus ground) power cord between the generator and the receptacle on the trailer (no power protection device) everything except the chassis of the generator itself has been bonded. 

If the generator is mounted on the RV then by code its chassis is supposed to be bonded to the RV chassis, which can be done using the generator ground connection point. That point is not connected to neutral at the generator receptacles, just to the generator chassis and outlet grounds. At least that's how my Honda is wired. Check your generator manual to be certain.

If the generator is not mounted on the RV and you have a circuit analyser that is looking for a connection between the ground and neutral conductors feeding the trailer receptacle, as StephenH says it will refuse to connect unless those two conductors are already bonded before entering the trailer. StephenH's bonding plug solution will work for that. A ground rod connected to the generator ground point would not, because the neutral would still not be bonded at the generator.

The only caveat I have is that the bonding plug needs to be able to carry the full current output of the generator. So if that is say 30A i wouldn't use a 15A plug and 12 gauge wire for that purpose. 

For myself, I don't use a circuit analyser when running on my Honda. Its not like there are miles of power lines waiting to be struck by lightning feeding into the trailer. The likelihood of getting a lightning induced spike on the 25 foot cable to the generator is negligible, and if it did happen the strike would be so close that I would be more worried about changing my shorts than fixing my trailer wiring.