As for the tail lights, the stock units were there, and were actually wired up when I bought the trailer (albeit incorrectly for the 4 pin it was using) but were very dim, even with good bulbs. I decided to use LED trailer lights (submersible type) to replace them. The challenge was that the lights I bought were designed to slide snugly into a precisely sized hole. No screws or otherwise. As such, they would not fit properly in the factory tail light position without some fabrication, or Jerry-rigging, at least.
Although this pic doesn't do a good job if illustrating the fit, you may be able to see the gaps on either side:
While contemplating the issue, I had the factory unit and replacements sitting next to each other, and realized that except for depth, the new lights actually fit inside the factory housing. With a little cutting and grinding, I was able to get the new piece to fit. This solves the fitment and mounting issues, as I can still using the factory mounting even after modification.
New light with black rubber (mount) removed:
Left light completed, right is "before":
Rear view, before and after:
Completed light mounted:
I'm pretty happy with how it turned out. The rear view isn't very pretty, but the "inner" light is still sealed, so no worry about exposure to the weather.
The one down side is that the Led's are now effectively passing through 2 red lenses, which does decrease the brightness some, but it is still an improvement over the original bulbs / reflector going through only the factory lens.