Waxoyl into inner sill?

[unclebeast]

My mate just welded up the usual spots at the rear end of both sills  on my Peugeot 405 and as I discovered a 5 litre tin of waxoyl and compressed air applicator i squirrelled away over ten years ago in the recesses of my shed.   Is there access to the "back"/"inside" of the sill to blow waxoyl on the inside cavity of the weld if I prise off the plastic trim/carpet inboard of the door or is it better to drill 10mm holes in the sill apply waxoyl and then knock in peugeot fir tree fasteners?

Photo before welding!