Frustrated with inability to do body work!

Yep.
Hard piece times two.
I do all my sanding body work outside.
This past week I cut, welded and replaced a lower quarter patch on a Duster Sport.
I used a snap chalk line as a sanding guide.
Seemed to work well.
But that was a straight line.
I also used a long sanding block for a straight edge and a lead pencil which made for a more durable temporary guide line.
I could replace either marking with a new guide line as needed.

On the OP car, what the eye does not see the body man gets away with.
Light sand and paint.
Find high/low flaws.
Lighter sand.
Paint.
Find flaws.
Still lighter sand.
Repeat as necessary.