I just did this and out right copied westend's design. I ran my solar, inverter and trailer wires to the bus bar. Going to the battery I have a Pos and Neg off the bus bars as well as I left my genny starter cables attached to the battery. This made for a nice clean wire setup with everything protected by the trailer frame and nothing hanging below the frame.
I ended up cutting and replacing the cable lugs on every wire under the trailer as they were to long to begin with. I purchase 2ga wire to run from my bus to battery but in the end I would have had enough just off the extra cable coming from the genny to make the bus to battery run. Yep there was an extra 4 feet of genny cable zip tied and hanging under the trailer on both the pos and neg side.
I also found that the genny neg cables was grounded to the frame and then attached to the neg battery post. After thinking about it and talking with a RV tech I could come up with no reason the genny needed frame grounding and removed this extra chunk of wire, now the genny neg goes directly to the battery.
I will post a few pic this weekend of my handy work.