How difficult is it to run wiring in foam walls in trailer?

2oldman, I don't see the inverter in that.

And profdant, don't worry, the newbie questions are helpful to me and, I bet, many others!

I will add that surface conduit, which is made for sticks and bricks wiring, is kind of giant for 12v wiring (and surprisingly expensive). You might consider getting some thick-housinged wire and just running it behind/through cabinets and stuff, if you can find routes where it will be protected. I am guessing that your rig is like mine and does not have a lot of bare wall space ;).