I don't care for parking my camper in the sun because it gets very warm, rather quickly. As a result, I'm quite happy with my suitcase solar which enables me to place my panel about 20ft from the camper and find some sun. It further enables me to adjust for maximum current and keep shade off the panels (you will be surprised how inefficient the panels become with just a bit of coverage over some panels).
My camper came pre-wired and it was fairly simple to just connect the right bits. I made my own cable for the panel to balance resistance losses with length and size (and also cost!) of the cable.
Everyone's use case is a little different, but we use very little power in our shell and it's usually charged upon arrival to our destination (two deep cycle marine batteries). It takes us about 2 - 3 days to use it (basically charging phones, LED lights, and the furnace in the morning, maybe a bit before we go to bed). I measure the voltage with a little voltmeter plugged into DC. This is highly unreliable and depends on a bunch of things like temperature and load (or even when you removed load), but watch it enough and compare the voltage to the state of charge vs. temperature chart I've printed out and taped to the inside of the battery door, and I think it's giving us a good feeling of charge.
We got the solar in case we stay one place with out any substantial driving for more than those two days, but it hasn't been very frequent for us. (But again, everybody's use case is different!