I agree that 12v solar array is the best... and no converter or inverter is needed for a 12v system. but you WILL need the solar controller, preferably an MPPT type, but they also have micro controllers now that connect to each panel separately.... I dont have any actual hands on experience with the micro controllers, but they sound like an easy way to go....
you are correct that if you have solar, you should have a battery bank big enough to maximize the system for the size of array you install...
there is such a thing as TOO many batteries for a given amount of solar capacity, so size it accordingly... which can only be done by knowing what your average daily amp consumption is, how much uninterrupted, unshaded sunlight the panels will get during the day, and the number/wattage of the array....
here in the northwest, I figure 8hrs of sunlight per day, and size the wattage of the system to twice what you require....
solar is by far the best way to create power for your RV (or boat), but the panels are rated in a temperature controlled lab, connected to a meter while they "short circuit" the panel... and the watts created in this manner is how they rate panels.... you will never see this figure in real life except under perfect conditions, using an MPPT controller, which the MPPT technology can take the output of the panels and boost it to create more input to the batteries than it would get by using any other type of solar controller.
so, in prefect laboratory conditions, a panel that is rated at 200watts has a theoretical potential of about 14amps.... but in real life, you will get a daily average of about half of this (usually a bit more), which is a good number to go by when figuring your system unless you never leave the warm sunny states.... when the system creates more power than the average number that you used, its a bonus, but when the sun is behind the clouds, or there is not as much sunlight per day, you should still be producing close to or slightly more than the number you came up with when sizing the system at 50% of its "stated" rating..... which would then be called 100% of the number you "engineered" your system to deliver on daily average...
the time and cost is in the wiring and the initial cost of the controller, wiring, framework and whatever else is needed, so as long as the space is available on the roof, doubling the size of the output is only a matter of the cost of a second panel, because everything else will have to be installed to run the first panel, and the second one and third one can be wired in, providing the controller you use is big enough to carry the load..
solar panel power is simple, clean, trouble free and with a long life expectancy, but if its undersized for your needs, you wont be much impressed with it, but if you have all the power you need because you installed a system that is big enough, no one will ever hear you say how you wished you would have installed a smaller system....
ive installed solar on my last three boats, and installed a system in a remote cabin for a friend, which both types of installation require that the system be able to support the needs that it was installed for, more so than an RV would, where you can either start the generator, plug into a post, or start the tow vehicle to get power restored into the batteries....