Whew. I took that thing off today and it's all solid w steel beams. The fiberglass you see is the side of the RV. There's no double wall there, just single pane.
I can't find any hidden recessed access to the front. I know I could use some cable management solution and get back behind the stereo cabinet door by drilling a hole. I could do that on either side.
There is access at the bottom though going down through the gray foam, so if I were to use cable management then going through the floor and straight up in an empty cavity would be a lot easier.
After I explored all that wing and bed area, I went back to the cabinetry where some cable area already ran and pried up a shelf that was stapled down, exposing a wire run. I found the point where the wire turns downward and heading to the floor in the back of the grill access under the stove and fridge.
Ok great, so now I can push/pull string and wire from that cavity up to the top cabinet and then forward to the awning wiring and an 18" jump to the 1.5" hole in my ceiling I'm using.
The fish cable I was using is perpetually stuck though on something behind the fridge and I can't free it up, so I'll have to cut it and I don't have anything on hand.
So my next strategy is to go UP from the bottom with some coat hanger wire and snag it at the cabinet access hole.
I'm with you on the jacketed 12 or 10 just pricing and guesstimating how much I need at that gauge. This is for the Lorex security system with DVR and 4 cameras, the wifi / Lte router, a NetGear Nighthawk and maybe other negligible stuff, @ around < 5A. I already have some regulated 12v PSU and Blue Sea power dist blocks I'm moving from my wrangler to the RV.