Wait and be sure you are not biting off a lot more than you should even try to accomplish. Step--by-step assistance is not a good idea when you are rewiring a trailer. You need some basic background in wiring and electrical
codes and techniques before even starting this project.
I would do the following two steps first.
1. Order a Progressive Dynamics PD-4045 Power Center. That's an all-in-one AC and DC power chassis, breaker panel, fuse panel and intelligent battery charger.
That's the heart of an RV's electrical
system. They are less than $175.00 on-line.
2. Then find an electrician that does outside work in the evenings or weekends, put the PD-4045 in his/her hand and point him/her at the trailer with a list of what you want to do.
Wiring a trailer from scratch is often easier than a re-do, but any mistakes, ranging from a simple short circuit, to damaged appliances, to an electrical fire can be a result and, like landing an airplane with the wheels up, it can ruin an otherwise pretty good day.