1) the plug is access to your fuel pump - you'd be permanently sealing it in.
2) The heat of welding would ruin the liner inside the tank.
A helpful hint: Use liberal amounts of grease when installing this plug. Sometimes I grease both the tank and the plug/o-rings, then spray wd-40 over the grease. The plug will fall into place with your pinky finger using this method.
The Vic Shop, Inc