Here is a web forum where the take cargo trailers and convert them into RV trailers.

There I am sure you can find out lots of information here on how to put things in.

http://www.mikenchell.com/forums/viewforum.php?f=42

here is a link to their electrical section. There is wiring basics and all sorts of things.

http://www.mikenchell.com/forums/viewforum.php?f=30


BTW... For my trailer I am actually considering a 12v system instead of 110v. Reason being is that since we lost PIR and 110 AC shore power I will be on generators all the time. Seems to me I don't need a generator cranking away 24 hrs a day. However a couple good batteries and some 12v lighting and I can probably run most of what I need. Thowing in some solar panels and I may be able to keep the batteries charged. I would run the generator only for bigger needs. I could use an inverter to convert everything to 110, but that is not efficient. Anyway you do it the site I linked has all sorts of ideas. They add insulation, cut holes for windows, add plumbing. Basicly all the info you need ot make your own toy hauler.

Seems like the biggest challenge will be determining what systems you need what you really want.