Get a sill they are about £18+vat, use what you need.
Make sure you have some MS sheet 1.5 section to bridge the bits that aint there anymore

Just boshing some plate on will make the sill covers sit all pissed and wonky

As above, take the seat out and peal back the carpet and insulation it burns real quick, squirty bottles to hand to put out fires.
If its had waxoil squirted into the sills at some point this can also cause a problem with choking
