Here's a few lessons learned via Ham Radio; building pro Sound Systems; wiring Trailers to haul Sound Systems in; and then fixing my own work over the years! Faulty wiring or Brake connections don't cut it when hauling around a Trailer full of expensive Sound gear.
1. The first thing I did was rewire my Utility Trailer DC with exterior Contractor Grade stranded extension cord. The outer sheath protects ample gauge wiring under harsh conditions.
2. Separate wires run inside Plastic Conduit will be well protected. Auntie M's idea is also a good one. This is how Avionics [Airplane electronics] wiring is secured.
3. AC and DC wires should not be run together. They can interact in all sorts of annoying, unforeseen ways. Someone using a power tool or blender on the same Shore power circuit as you can induce 'hash' into your DC Electronics [Radio, TV, etc.]. Inverters, including your own - should you ever use one - can do the same as DC and AC wiring interacts in close proximity.
4. My $0.02 worth is always run a separate, adequate wire ground back to the Battery. Skip using the Chassis. The ultimate, and only ground is either the (-) lug of a Battery, or the 3rd prong ground on AC Shore power. Multiple grounding points can raise havoc. Chassis connections corrode, and it takes only a fraction of an Ohm in additional resistance to affect some circuits. This is one reason Electric Brake Manufacturers suggest using a separate ground wire and/or connector pin for the Brake ground. This technique also prevents Brake and other Trailer, high current flows [like remote Battery charging] from interacting. We 'overkill' types run all wiring back to a weatherproof junction box, or a Breaker box. This allows [re]connecting ground wires in different ways to eliminate ground loops, etc.. However, this is done usually in complex Audio systems. A Trailer with plenty of Entertainment or Solar equipment would be a candidate for such 'flexible' grounding connections, not hidden in walls. For a simple TD, such steps are typically unnecessary. Alternately, 'pro' diagrams from RV Solar Installers reproduced in these Forums are tried-and-true.
5. Despite how widespread they are, I've given up on Cig Lighter-style +12 VDC plugs. The small center surface area is OK for low current draw Accessories. With high current draw items [like Trouble Lights], the connections overheat, corrode and fail. Consider converting +12 VDC connections over to right angle Blade plugs, as used on Honda Generators. Then, make yourself one or two Blade -> Cig Light connector convertor plugs to be used only in a pinch. Having more contact surface area, Blade plugs can safely carry much more current [Wattage].
An old trick is to run parallel, more easily manipulated wires, to achieve the performance of larger gauge wiring. For example, 2 - #16 wires connected in parallel roughly equals 1 - #12 gauge wire in Trailer length wiring runs. See a wiring chart to confirm the Ohms/1,000' of a given wire gauge. This trick is especially handy when wrestling with very large gauge wiring.
http://www.powerstream.com/Wire_Size.htm
I twist, solder and put Heat Shrink Tubing over any exposed connections. Leave a loop of wire at the end of a run, when possible, so that connections can be re-made if a Tail light has to be replaced, etc.. With a clip on heatsink [to avoid melting Insulation]; clean initial connections; a plumbing Torch; good Flux and Solder, even large Battery spade lug cable can be soldered for greater lifetime reliability. In my experience, you either do it right in your Garage or Driveway, or redo wiring in lousy weather at the roadside.