I did not go for the factory solar panel on my 2004 Hawk, Shell, 4WheelCamper. Maybe I should have, at $560 installed it is a reasonable price. I found installation on the roof of a pop-up to be more difficult than I had imagined. Also my 75watt BP panel cost about $1000. I found the 75watt solar panel to be very useful, in sunny Australia, not so useful in rainy BC.
If you plan to do lots of multi-day trips (that don't involve a lot of driving) in sunny climates, some type of solar panel is a great idea. Is 50 watts enough? I don't know. 125 watts would be great but......More power = More$$$
Perhaps you could try the 50 watt panel and add a second 50 watt if you find you need it latter?
Cheers
Mark