We have a 200 watt setup for our camp trailer. Home Depot for about $300. We can add up to 2 more 100W panels with the same controller.
SOLAR KIT 200W will fully charge our 2 golf cart batteries from 50% in about 2 hrs on a sunny day.
It comes down to 1 thing: the more power you need, the bigger the setup has to be. Each panel in this kit is 31x42" and outputs 100W. This kit comes with 2 panels. You can add more panels or buy a larger kit to start with.
With RV's many people mount them on the roof. That has 2 problems. 1, lying flat they're not at the optimum angle for the highest output. 2, you always have to park in the sun. I'd rather park in the shade. I used some aluminum angle and made a portable stand that holds them at about 45 degrees. I can easily turn them as needed and I made an extra 50' cable so I can set them in the sun away from the trailer.
There are 2 types of controllers. The cheaper one is called a PWM, whatever that means. It'll handle 400W with no problem. The other one is an MPPT. They're more efficient and will handle a larger load but you'll pay a lot more for one. Your choice. This kit comes with a PWM and it works fine for my purposes.