RV parks catering to the RV crowd might have the higher power supplies.  BUt the horse camps I'm at, are a bit less inclined.

They only have a 30 amp service at the most.  Some have two 20 amp receptacles.  I chose to wire my horse trailer for two 20 amp inlets.  Each serves a single circuit.  I bonded only the grounds and the trailer together.  Otherwise the circuit's neutrals and hots are isolated from each other.  Any other way trips GFIs at the power post.

hosspuller - can you elaborate on this set-up?  I also have two 20amp breakers.  One for the a/c only, the other serves everything else.  If I plug into a GFI outlet with my 30amp cord, it trips.  Non-GFI, no problem.  Have not been able to isolate the problem, have checked all outlets, etc.

Thanks

Sheryl .. 

First be safe, unplug your trailer, double check... Since you say you have "a" cord I'm assuming you've got a single 120 volt plug.  Then, Look in your breaker box.  The white(neutral) and the ground (green) are likely connected together.  They will need to be separated.  The ground (green) should be connected to the metal of the box and the metal of the trailer.  You might have to break a metal strip (tie) and move all the greens and the whites to separate bars.  ASK someone knowlegeable to check your work if this doesn't sound familar.

Most of the horse camps that I go to do not have 50 amp service. If you install a 50 amp service and plug, be sure to have a 50 to 30 amo adapter with you at all times.

Concerning the question about the GFCI breaker trip, you might need to check all the receptacles in your trailer even if the neutral and ground at the box has been seperated. I have seen a bare ground wire come in contact with the neutral conductor inside the box. The best policy is to put electrical tape around the receptacle covering the bare screws so the ground can never come in contact.

Sheryl ... The fault Rooster suggested, would not be indicated by the plug in outlet testers.  So if the path I suggested still doesn't fix your problem. get the receptecles checked. 

It might be faster to check the path between ground and neutral with a Ohm meter to see if there is a connection/short.

No .. Connecting the bare copper ground wire to the trailer frame is correct and proper.  Otherwise you could have a dangerous condition where the trailer is charged by a fault and insulated from ground by the rubber tires.  When someone then touches the trailer (Like opening a door) while standing on the grass, they get electrocuted.

Justinc : I believe your problem is the white wires (neutrals) of your two circuits are connected together.  The GFI is looking for an imbalance.  If current flows to the neutral of your other circuit, that's your imbalance and the GFI trips.  The neutrals of your two 120 volt shore circuits must be isolated from each other.

Whoa !  Is the GFI that's tripping in your trailer or the campground power post?

I'm having a hard time understanding what the Levitron tech said to you.

The neutral and ground have to be isolated when plugged in at public campgrounds with GFI.  I went through the same frustrations with a new used trailer that had been wired by previous owner.  RVs went to the 50 amp service to provide power to run 2 air conditioners at the same time along with power  for washer, dryers etc...  prior to the super huge motorhomes and 5th wheels with all the options almost all rvs ran the 30 amp service.  Currently most entry level rvs still use the 30 amp service.

I've been fighting an problem on my new trailer where it always pop's the GFI plug when I connect it to my house or my 20amp generator.  Everything ran just fine IF I plugged into a 30amp or 50amp house hold plug. After reading your post, I opened up the circuit break panel and looked in

There was a common block for the white, a common block for the Ground and all the blacks went into breakers. At first glace everything was in the right place. White on the white bus, Ground on the other bus.  But as I looked closer I found one ground wire was brushing against the bus that the white wires terminated on. I carefully bent the ground wire away from the bus.

Now everything works. I don't pop the GFI when I plug into the house.  My Yamaha EF2400is will run my Carier Air V A/C unit just fine.

Thanks for the tip.