I was never able to locate where I could tap the 3 pre-wired outlets. I ended up just wiring all the 15a non-GFI outlets to the inverter. I just grabbed the outlet wire from the breaker box and made that the output of the inverter via a transfer switch. The other input to the transfer switch then came from a new wire off the 15a breaker that was originally hooked to this outlets.
Now when on shore power the path to the outlets is through the breaker box and when not on shore power the transfer switch hooks the outlets to the inverter. Works just fine this way. Not worried about too much draw off all these outlets since all they run is the TV, a CPAP and maybe some USB chargers.