Additional solar panel to system

I know there are a few electronics experts on here who may be able to help me with this.

We have an Autotrail van which came with a factory fitted 100 watt solar panel. The internal electrics are all controlled via a Sergeant unit that can only accept up to 120 watt solar input. The info panel connected to this unit is very good as it displays a variety of readings including solar input, battery voltage and percentage of battery capacity remaining. I don't want to lose any of this info.

I am considering adding a second (similar sized) panel and connecting it to the batteries via an mppt controller.

From reading other posts on Motorhome craic I see the use of an mppt controller makes a great deal of difference to the panel output.

So, would i be better connecting the original and new panel to the mppt controller and using it for the solar input reading or leave the system as it is and adding an additional panel and controller to charge the batteries before the original system gets a reading?
I can't see the second option being an issue as the control panel will just assume that the batteries are getting less drain than they actually are. (Or am I wrong)

Any of our experts able to say which is best?

I'm no expert (far from it), but I would forget about the Sergeant Controller and fit a good quality MPPT that is able to handle the input and use that for both panels.

Def remove it from the Sargent unit, a good quality mppt with a remote display will tell you what is going in to the batteries and the onboard will tell you what’s going out. On my old Knaus I fitted a remote display unit and spent a lot of time worrying about what the panel was doing, on this van I don’t have a remote display and never worry about it!

Figure out whether you want to wire the panels in parallel or in series as there are benefits and issues with both

Expect to pay about €100 for a quality MPPT charge controller which would handle 300w of solar. Beware that there are some lesser priced controllers sold as MPPT which are poor quality or worse still are in reality only PWM units with MPPT stickers.