That depends. I've had solar on all three of my RVs. As to being cost effective - not hardly. You pay a lot for the few amp-hrs you get.
Yet, I still have them.
480 watts with the OUtback controller, flat mounted. I don't know if tyher will be physicall room to locate the larger 165 and up panmels on an RV. 125 watts is usually all that can physically fit given the junk that's on the rooftops.
Running them in series, rather than parallel is great. I t keepsd the wire gauge down. You do need the Outback controller though because it can take a 60 volt array and output it as 12 volts to the batteries. It's the best charge controller out there- bar none.
Remember, solar panels don't "run" anything. All they do is try to oput some amp-hrs back into your batteries. You will need a large battery bank to make effective use of a solar array. Eventually you are going to have to run the generator anyway but solar can extend the time between recharge cycles so that it's more convenient for you.
As to cost effective - hardly. It take a decent sized system in order to get any real benefit and they aren't cheap. But, for the right person with the right circumstances, they can be a nice improvement and will make for smoother sailing as far as power management is concerned.
If money is tight I'd recommend ugrading to more battery capacity and go with AGM batteries. AGM batteries have less internal resistance, no water to ever check or add, no outgassing of hydrogen, and have a flatter voltage drop overtime curve that will give you about 30% more runtime from an equally rated flooded battery.