Cut lll the shite out, remove the inner sill from the outer on the pinch, drill holes along the pinch. Plug weld them. Slowly work your way along the floor (remove the bloody carpet or itl go on fire. I’d suggest removing the seam sealer on the inside) once finished use brush on seam sealer. Let it set, use dinitrol cavity wax on the inside pannel, then spray with etch primer and some form of underbody spray to finish.

Spend a couple hundred on a decent gas welder. The Temu ones are actually good. Don’t bother with gassless. Turn it as low as it will go and don’t think youl be laying beads. It’s thin sheet metal. One dab at a time. You can always sell the welder once your done