You can also use rivet inserts, aka nutserts. No welding is required. Simply drill the hole and insert the nutsert (do not drill the hole to big!), install the correct size bolt with a flange nut on it. Put a wrench on the flange nut to hold it from turning and be sure to keep the nutsert tight and flat against the frame then tighten the bolt. The flanged side of the nut will set the nutsert in the hole. The bolt is hard to turn at first but you'll be able to tell when it is set, you don't want to over-tighten it.
I would check McMaster-Carr.com or a hardware store that sells specialty fasteners for the nutserts, bolts and you only need one flange nut.