Standard SMB Wiring Practice?

[DVD]

Since I couldn't replace just the lampshade on one of the house lights (would have to buy the complete light), I decided to switch out to LEDs. Got some nice lights from Superbright and went to install them today. The first one, above the rear doors, was straightforward with a red and a white 18G wire which I hooked up to the new light just fine. The second one was the light over the sink. When I took it down I found two 10G wires, black & white, butt-connected to short lengths of 18G wire then wire nut connected to the lamp. Along with the 10G wires was a very small wire with clear insulation (20 or 22G), which looked like antenna wire, and was also connected to the light:


The third light was the overhead one just inside the barn doors. When I took it down, I found 2 black duplex wires that look like 110V household lamp wire. One wire from each is stranded together then connected to the lamp with a butt connector.


So this leads to a couple of questions.
1) Any idea what the small 20-22G wire is going to the over-sink light?
2) Is this type of eclectic wiring normal for SMB and can I expect to find more surprises like this as I work through the van?

This is my first land-based RV - all my other toys have been/are large boats. I have never seen a build like this in the marine environment. Standard on board electrical practice, even in a protected, interior environment is to use a waterproof heat-shrink butt connector, then cover that connector with another layer of heat-shrink tubing, secure the wire from vibration and label it. Wire nuts just don't hold up to vibration and the environment.

What I am finding on my 2005 SMB looks like it was put together without a lot of skill, using whatever was lying around the shop.