I keep popping the GFI plug when I plug into shore power

A Scotch-Loc brand wire nuts are often times hard to remove when necessary.
I've had cheep wire nuts fall off while pushing the wires into the electrical box right after putting them on.

Thanks for all the responses guys, this forum is freakin rad!

Yup wire nuts can literally back off and unscrew overtime from getting hot and cooling down cycle after cycle after cycle.

Hey Rock Bottom, I'm just down the row from you at AVRVS, space 177. I'll be out to Simi one day this week. If you haven't solved the problem by then and you're home, I'd be happy to drop by and take a look with you. Pm
M ME.

Either way, It would seem that your GFCI outlet is good and so it seems is yourextention cord. I'm with the suggestion that you disconnect the circuit from the male connector to the main. Wgriswold gave you a good starting point.

Sometimes starting at the beginning takes more time but it is usually fool proof.

If the GFCI pops with the main breaker off, it could be a problem is the shore power cord, or could be a neutral-to-ground fault in any of the circuits beyond the breaker panel. To locate the problem, the only way I know of is to disconnect the neutral wires from their bus bar to isolate which circuit the fault is in. If you're ok messing with the wiring in the panel, ok, otherwise find somebody who knows what to do.

The same thing happened to me with my 2001 trailer. The problem was the connection where the shore power cord connected to the trailer. It was in a junction box and the connections were with twist on wire connectors. One of the wire connectors had worked loose and the connection was bad and the wires had burned back about one inch.

I cut the wire back and reconnected with a new twist on connector and wrapped the connection with electrical tape so it would not come loose again.

I learned in my boating days that twist connectors are a bad idea in vibrating environments. I should have used a more robust connection but didn't have time.

Open the AC circuit breaker panel inside the RV

OPEN Every Circuit Breaker inside the panel

Try plugging in to shore power....
IF GFCI trips then it is the 'adapter', the extension cord, the RV Power Cord or incoming wiring going to the RV Power Panel (mice/squirrels LOVE chewing on the wire insulation)

Thanks for all the great informative responses you guys! I went out and unplugged the fridge from the access panel, reset main breaker in the camper and shut it off, still pops the GFI instantly. I saw the response that if it's popping with the main camper breaker off that it's got to be the cord, so I retried with my other extension cord and same result. So am I to understand the RV cord is looking to be the culprit? I read online that it could also be the charger on the converter. I already have the link saved for the upgrade kit for my converter, not scared, just trying to get to the lake in a few weeks and still need to buy my tiedowns so don't wanna spend money I don't need to lol

First I'd upgrade that Magnetek to a Progressive Dynamics (Just the electroncs in back of the fuse/breaker panel. 4600 Series at PD)

Next: a GFCI is not current sensitive in the manner of a circuit breaker. Just as I got back from Church and shopping today power "Blinked" one of my A/C's tripped the circuit breaker as it was trying to re-start with a full head of pressure. I re-set it after it had time to bleed down a bit and all is fine.

That breaker tripped because that A/C can draw over 20 amps stalled compressor.

Circuit breakers however are like a balanced teeter totter. Perfectly balanced neither end touches down .. The GFCI measures current in both the black and white (not and neutral) legs. and so long as they are balanced.. It just sits there and observes. (passes current) but if either end "Touches down" (If the current in one let is even slightly higher than the other CLICK and shut off.

So fast you won't even have time to feel the shock

The sparking when you polug in.. Normal believe it or not.

The tripping of the GFCI. not

TUrn off all breakers inside the RV. now plug in and also if it's a duplex outlet plug in a drop lamp or other light you can see WHILE at the breaker panel.

If it does not trip. Great
Turn on first the MAIN breaker.
then one at a time turn breakers on till the light goes off.
Identify the last breaker you turned on.. Turn it back off. Reset the GFCI (light back on) and continue till you have tried EVERY breaker. the breaker(s) that turn off the light. Report what they are.

Some converters (I DO NOT KNOW IF YOURS IS AMONG THEM) will trip a GFCI if the batteries need charging.. Others (SAME QUALIFIER) if they are full. Some all the time and some never (Again Same qualifier all 4 times)

I only know for sure ONE and .. that's a Progressive Dynamics 9180 with Charge Wizard. I assume other PD's (Does not trip GFCI) but I'm only 100% sure of ONE. and that.. of course.. is about 25 feet from where I"m sitting.

Your ground fault or short has nothing to do with the 12v fuses so don't bother with them. Sparking sounds like a short to ground. If you have the camper main off when it sparked it has to be in the cord.
You don't need a heavy extension cord to trouble shoot a ground fault or short. Even a light duty one will work if you have it.
You either have a neutral touching ground causing a ground fault or a hot wire touching ground causing a short. A direct hot to neutral short would not trip the GFI but would trip your circuit breaker feeding the outlet.