yeah I would suggest welding either or patch or just a tack depending on how big the holes are. then body work, prime, paint.
Do not prime the whole trunk, keep your body work area and primer to a minimum so you will be able to blend the paint within the panel and not have to worry about blending adjacent panels or your color not matching.
If you cannot use a welder, tap the holes in a little bit to create a small dent. scuff the area thoroughly with 24 or 40 grit paper. then use short strand fiberglass filler, then do your body work. prime and paint.
2010 Cobalt LT 4 door