Interesting thread, lots of good information. Thought I'd just add my 2cents worth based on my experience, but little real or useful knowledge
Currently we have a 15 to 20 year old solar panel mounted on top of our 2004 Trillium Outback, measures about 2ft by 4ft and is either 80 or 90watts, BP cells. Had it such a long time that I've forgotten a lot of the details, have used it on several RV's and this trailer plus used it to charge a battery that then automatically powered outside garden lights when it got dark(a time with no RV
The dealer installed it for us on the Outback. So, looks like they used 14 gauge wire, not the best. Runs from panel to regulator is about 5ft, then about 9ft to the battery area. The regulator is a Soltek 20Amp unit and displays the battery voltage and charge amps alternately. We have two Alliance A105-5 6V batteries that are now 8 years old.
I just went outside and looked at everything, the batteries are slightly frozen on top, normal in our cold winters. The panel is putting out 1.5 amps in bright light facing away from the Sun, batteries sit at 13.4V, then turned on the DC fridge and a light dropped to 12.9V, recovered quickly after turning them off. These batteries have seen a lot of heavy usage and have never been a problem, I can use a lot of power when doing astrophotography, PC, Camera with cooling, telescope drive plus the fridge is DC only. Have never run out of power even after dry camping for a week. I check and add distilled water a couple of times per year at least.
Right now we're debating on taking the system off our trailer before we sell it in the spring and keep it ready for our future 19ft Escape, September delivery. Need to talk to Rease about how we'd mount it to the roof though. I really like having it continually charging the batteries, in the winter just brush the snow off the panel and it goes and goes.
Steve and Mai