Adding a solar panel

If you buy a panel and matched controller then you can attach direct on the battery with no issues.

If you want to run the added power through the existing controller you will need to verify the existing controller is compatible with the total wattage and voltage.

How well does the existing 100 watts work for you? Can you make it through a weekend and keep battery charge above 50%?

You will want a smaller size panel if you will be moving the RV often and carting the panel in and out to place it outside. A bigger panel on the ground propped up towards the sun is better for getting in the AH, but more for if you are staying in one spot for longer periods as a practical matter for handling. (still need to carry it somewhere when on the road though)

You can add the new by just connecting its controller to the battery bank in parallel with the old set--but try to get the two controllers to have about the same voltage so they add their amps.

Your 200w choice will require an MPPT controller and the one now is likely a PWM, but they can work in parallel on the battery set to the same voltage. A 100 will likely just go on the roof with the other one and share its controller--but-

If the choice is to add the new panel to the old, then you have to check the controller's specs to see if it will do all those amps and beware of series where you add the voltages--the controller's voltage limit (total of panel Vocs) could be reached and fry the controller. Parallel is not an issue for that.

There are no issues using a portable panel with your existing system.
To give you a rough idea, I have 200 watts and boondock for 30 days at a time. I don't use the TV, just use water pump, furnace at night, exhaust fan when showering, LED lighting for about 2 hours per evening and charging cell phone and flashlight.
My batteries (two-GC2 6volt) are usually sitting at 80% SOC in the morning and are at 100% SOC by early afternoon.