Your lights are usually 12V, so the problem is likely to be your converter. If the problem is with 120V lamps, try removing the lamp in each fixture. If that doesn't ID the problem, you are going to have to "unwire" each.
Some general information:
Your trailer should be capable of operating plugged into a GFCI receptacle. In fact, if you visit some of there Missouri State Parks I've been in , ALL the receptacles (20, 30 & 50) are on GFCIs.
There are a number or reasons GFCIs trip. A bad water heater or refrigerator 120V element can cause the problem (and still be working). Water in a receptacle (particularly an outdoor one), a faulty appliance.
If you want to find the problem, the first step is to shut off all the breakers except the main. If that stops the tripping , turn each one on one at a time to find the circuit causing the problem.
If the GFCI trips with all the breakers switched off, you have a ground/neutral fault. Much harder to find where since there is no breaker to shut off. If you are comfortable with your fingers in your breaker box, lift the neutrals one at a time (with the main breaker shut off). When you find the one that eliminates the tripping, check th devices on the circuit.
