Have had a solar panel on our trailers spanning 30 years. As a retired EE, this stuff was easy to do. For last 12 years have also a 5k solar array on our home feeding the grid. Now to share thoughts from our experience.
1. A solar panel only needs to replace charge lost due to consumption since the last charge. When dry camping that's often very little, especially when using propane for cooking, refrigerator, and heat in your trailer.
2. We usually camp in sunny locations. If A/C needed, we look for hookups. Solar isn't a viable solution. If camping in shade, portable solar required.
3. Never had more than 2 matched batteries, usually they last 5 or more years.
4. Mounting the small 7amp regulator in the refrigerator back access panel worked great for our 19 foot Prowler since the wiring passed through there anyway. The panel was 25 watts. Max current draw was negligible at that wattage. Have a 30 foot trailer with superslide these last 12 years and a 65 watt panel with electric jack. It's controller is mounted behind our front frame member.
5. We're not wasteful, of course, but we've also not had dead batteries.
Hope this encourages you.