I do this deal all the time. Get one of those spot weld drills and drill out all the spot welds holding the apron on. Use an air chisel to bust them all loose. Fit in the new apron (they are cheap) and drill holes in it to duplicate spot welds and weld in the holes with your MIG welder. Paint and your done. Assuming you have all those tools..................
You could patch the bad part using the new apron material, but that would actually take longer to do unless you just want to slap the piece on and weld it.
All depends on how you want it to look. I always replace.
Hope this helps.