Whenever I plug my trailer in using an extension cord (heavy duty), flames and smoke shoot out at the cord/adaptor sight.  I am using the best adapter on the market and have gone thru 3 cords. This is without anything running inside the trailer.

I have had two electricians look at my trailer and they can't figure out the problem.  When I plug into my generator (not using an extension cord), I constantly blow breakers on the generator.  Is this an inverter problem?

You have an electrical component that is internally faulty or wire that is directly shorted to ground. It will take some trouble shooting to determine the area and the cause. A qualified electrician should be able to determine the problem.

Gard

Is this trailer new to you, or has it worked well and this problem has recently developed.

I had an electrical issue at one time that, after very extensive testing, turned out to be in the actual electrical cord (not an extension) itself.  Replaced that shoreline cord, and all remained well for years.  And that cord that had the problem looked flawless from the exteriror.  Good luck with this, and a vist to an experienced licensed RV dealership shop is where I would start.

I've owned the trailer for 4 years and this problem recently developed. 

So do you think it's NOT the inverter?  That is what one of them suggested changing out.

The inverter could be a problem. Any component could be. You don't have to replace it to find out if it's faulty. Just disconnect its power source. If the short goes away, it was probably the fault. Further trouble shooting will verify the situation. If the situation persists, it's not the reason for your difficulties.

A qualified electrician will trouble shoot your system to find the problem. He will use a multi meter, test light and intuition. He won't indiscriminately start changing expensive parts to find the problem. Find a qualified technician, and he will save you money.

As another posting states, start with the power cord and work towards the trailer.

I've reread your posting several times and have a question. You say that you are plugging your cord into numerous extensions and the generator, and yet you have the same problem.

Are you talking about the same plug on the end of the shore cord? If you are, I would first check the plug itself. With age they can be stepped on and crushed, the pins can twist under the cord's weight or pulling in different directions. They can be damaged internally and short out, whilst still looking well externally. They are replaceable without changing the whole shore cord.

If the plug is well, the cord then should be also checked. It too is subject to mechanical wear, from feet, hooves and vehicles. The insulation doesn't have to be abraded to indicate an interior short, but it may do so. This too should be carefully examined and its length rung out for shorts and continuity. The next area is the trailer's interior. Once you're inside the trailer, the trouble shooting difficulties increase.

Gard

Your main problem are the two electricians.  They aren't qualified or not equiped for your trailer's problem.  Find someone who is.