The splice points are made out of Raychem heatshrink and copper pipe fittings. You can buy ready made "T" fittings that are basically molded pieces of heat shrink, but they are expensive (~$20 a piece). I improvised and soldered copper Ts together, painted them flat black and closed them off with heat shrink. For the straight splices, there is a piece of 1" copper pipe inside the heat shrink that helps it hold a nice clean shape as the heat shrink is shrunk down. I've used this type of heat shrink on several trailers for several years and if you use the kind with a heat activated glue on the inside, it will give you a water tight wiring harness.
On the sealed lights, you may have to replace the whole bulb assembly when the bulb burns out, but the internal fixture will not rust like the cheap, generic type will.