Rusty (I)
Rusty rear valance? Can't weld? Don't pay a garage megabucks for welding and respray - just grind your old one off and pop rivet a new one on!
The valance is not structural (that's why it's left off some racers) and so pop rivets are enough. Then you can slap some underseal on and then hey presto! You could even underseal all those hard to reach places under the boot floor whilst it's off too!
Rusty (II)
Simply attach a new valance using the 3 bumper studs.