The n/side sill was done last year when I had the skirt and back bumper off off to weld a couple of small patches into the rear wheel arch. I noticed the rubber mastic stuff on the sill seams had split and was letting water in there to attack the floor pan.
That continued into that seam between the boot floor and the wheel arch and round to the outer rear arch (bubbling under the paint). It took a few weeks to sort all that out.
Offside wasn't affected quite so badly.. I patched up the mastic inside the wheel arch but didn't get round to removing the offside skirt... but I can see the mastic is splt along that seam too. Luckily, the floor is still in good nick, so it'll be just a strip and replace of the mastic (hopefully!).
Under the tank/floor looks splendid, though the towing hook was a bit nasty. A whole bottle of Ku-rust later.. sorted!
Apart from the rear-sub and the slightly dodgy offside sill seams, only the front subframe lets the side down. I may have that beast off too... but all the second hand sellers want £90 for the front sub-frame (Fiat Marea, Alfa 145/6 all fit)... so I'm still looking. Mine *may* clean up... but it'll be quicker to get everything I need, then swap old for new in one or more weekends.