So we had a small 50W panel which to start with we plugged into a socket mounted on the rear step. This was ok, but we did have to keep messing about with it, find somewhere to store it each trip so to copied others and put it on the roof. It came with its own built in controller but that couldn't fit with the roof mount, so we bought an eBay 'MPPT' controller.
The setup worked for what we wanted, but the following year on a trip across Germany, we found that without running the engine every couple of days, the batteries were running flat, the panel couldn't keep up with the fridge requirements. On our return, we resolved to add another panel, bought an additional 80W and fitted it in parallel. This was an improvement, but the following year, one of the batteries died, just before we were heading off to Europe again. We limped round France with one battery and the panels, but there wasn't enough power coming out of the panels to run the electrics during the day and charge the battery.
We returned and replaced the batteries, and once again we were ok for a while, but these batteries really didn't last and two years later they were dead. As things would have it, just before we went to France! Two new batteries purchased on the way, but it was a similar story, not enough going into the system to keep everything going during the day, and keep the batteries topped up.
Well, things to think about, new panels, what about the controller, and better B2B. There'd been some chat on forums about dodgy solar controllers, and a picture of ours was shown as one of the culprits. So pulled it a part and confirmed it was a piece of junk just as likely to damage batteries as charge them, with poor regulation from the panels.
Next up, replace the lot