OP, get yourself an NCVT - non contact voltage tester. You just need to hold it near a wire to see if it is live.
I would sketch out a plan of your unit and show which working receptacles are on each particular breaker and then shut off the still working circuits, pull the known receptacles without power out of the wall and start tracing the circuit(s) that isn't working. You may find some help on the panel directory but they're typically not very accurate. If you pull a receptacle out of a wall, you will find that the wires are connected by pushing the wires onto a "stab" connector at the back and are not screwed on. You don't want to pull these off because they need a special tool. I have seen wires on the back of an RV recept. barely hanging on due to faulty installation. It is possible that you have a wire that has come off. If it has, you can push the wire back on with a flat blade screwdriver and/or pliers if you are very careful.
If you pull a recept. out, you can use the NCVT to see if the load side of the GFCI is live. I have heard of some people having an outlet box with splices in it buried somewhere they never knew about and a connection has come apart. You could possibly also have another GFCI you haven't noticed like say at the fridge or even behind the microwave.
If you test a GFCI with the NCVT and find that the load side wire is live, then the other end of the wire should show up at another receptacle somewhere. Just go around with the NCVT and find the recept. that has a live incoming wire at it. If the outgoing (load) wire is dead, then you know that something is wrong with that particular recept. It is very unlikely that you have a severed wire anywhere, but it's not impossible.
You also say that some 12VDC lights are working and some aren't. That doesn't quite make sense. The lighting is on a different system and it's unlikely that you have both 120VAC and 12VDC power problems at exactly the same time. I trust you have checked the 12VDC fuses? I would focus on the 120V receptacles first and go from there.
Is the inverter on a dedicated fuse or breaker and what does it supply power to? If you have a voltmeter, you could disconnect the output of inverter and see if you are getting 120V out. One possible scenario could be that the circuit the lights are out on was connected to the inverter input and also that the non-working receptacles are fed by the inverter?? All it would take is for that one fuse to blow and all that you say is not working would be related. Is the inverter a mod. by the previous owner or are you the original owner? Maybe a PO did something not quite correct? What inverter is it?
What is your unit? Some pics may help.
