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Having two sets of panels wired in parallel doesn't cause a problem as long as both sets operate at the same voltage.
But you have two sets of two 12V, 100 watt panels and you want to add a third panel to one of the sets. That won't work. If you wire the new panel in series with the other two, you will now have 36 volts nominally. The other set is 24 volts. That won't work with your MPPT controller very well.
Another way to do it is to buy a 24V nominal panel and wire it in parallel with the existing two panels on your roof. That should satisfy your controller but it may not be possible to buy a 24V panel that will fit as they are usually 150 watts or greater and are often more expensive due to shipping costs. Also they may exceed your 30 amp controller's spec.
That spec is how many amps it can deliver to the battery. Batteries usually are charging at about 13 volts, so the maximum wattage to the battery is 13*30=390 or 400 watts nominally. 500 watts of panels will exceed that rating.
You can do it safely only if you never use your roof top panels at the same time you use your portable panels. So if you can fit a 24 volt panel in the space and live with that restriction, then you should be ok.
David
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