Need Inverter Install Help

You've hit on what I was getting to.    Modified sine wave inverters can't function with the neutral bonded to ground.  Home wiring, and campground wiring, have the neutral bonded to the ground at the main panel by code, but it isn't in the camper.  MSW inverters don't have that bond internally (PSW do), but attaching the MSW output in parallel with the camper wiring while it is plugged into your house exposes it to that common bond in your service panel.  Unplugging the pod from your house should allow the inverter to power up without throwing any breakers - but BIG WARNING, in your current configuration I'm worried that you are backfeeding your pod's 30 amp plug if I'm reading your post right.  So it will be live if you try this.  As Keith-N-Dar said, you'll need to install a transfer switch (one that breaks the neutral and not just the hot line) to allow it to power the pod, or wire the inverter to its own outlet and just run stuff from that outlet.  

Thanks Sean.  That is what I was thinking but didn't say it well.  Like a transfer switch for the generator home hookup so  you don't fry the guy fixing the power lines.

If the inverter AC leads are lifted from the breaker you installed in the Pod and the problem goes away look for a ground path in the output side of the inverter.  Without prints I can't guess at what you have.  Doug is most likely more able to help on this, but assuming correct hookup there may be some incompatibility between the inverter and ground power (such as a path to ground that trips your GFCI.  

Your installation has created a ground path that didn't exist before.  I would start with the connection from the inverter to the AC side of the Pod.  Lift those connections and see if the breaker still trips.

Is this a modified sine wave or pure sine wave inverter?  Is the pod plugged into a GFCI, or do you mean the GFCI inside the pod?