The inner wing has very little paint and no under seal let alone rust protection , if the plastic wheel arches are missing there is nothing stopping the crap and then corrosion forming.
The best solution is to remove the outer wing and drop the suspension down , clean all the rust off , treat rust killer then with a zinc inhibitor, then hammerite , then a decent underseal.
I had no signs of rust but recently did mine as a precaution although i didnt drop the suspension i sprayed a rust inhibitor all around there and then brushed underseal on top.
This is the amount of paint under the arch!!!
There is also only a thin coat of paint on the inside of the outer wings
These cars are timebombs for corrosion