Its a pretty easy process these days as compared to just only a few years ago. There are many many folks using solar panels now on RVs.
It is in my plans as well for a 120WATT Solar charging system for my OFF-ROAD POPUP roof to run with my 2KW Honda generator to keep all of my batteries charged up.... My game plan for camping off the power grids is to run all of my 120VAC and 12VDC desired toys from the right size battery bank and then keep my batteries re-charged with my 2KW generator being run for a short three hour period each day. Having solar panels would really help this situation for us.
This is a simplified diagram what is required and they come in kits now... They even have sticky 3-M pads to support the panels on the roof now which means NO drilling holes. Like the other post said the hard part is getting the cables down to the batteries without drilling holes in the roof. The solar panel idea will integrate very well with the on-board smart mode converter/charger system.
This would give me solar charging when the sun is out during the day and I would need to run my 2KW Honda generator less often to keep my large battery bank charged up when allowed to run my generator at the camp sites..
It seems that most public operated camp grounds all have generator restrictions of some kind or another and even the Natl Forest have them as well. Running off the batteries for these remote camping off the power grid areas was the answer for me but I need to be able to re-charge the batteries the next day to at least 90% SOC to be able to do it all over again for the next day/night battery run.