how to smooth body after getting to metal

[AmadeusCharger500]

I have a roadrunner hood I sanded to metal. I was unsure of the roll on paint that was on it so I took it off.
So now I am left with the uneven bare metal. I thought I would do the same thing I did with patch panels and put a thin layer of lightweight filler but it is so time consuming just applying the stuff. I use an 8 inch paddle and I can only get about 12 by 12 inch square done before the stuff hardens.
Anyone have a way to do this that is more practical?
Spraying with thick primer sealer is what I am ready to do next, unless someone can help me here.

[400/6/PAC]

Time and hard work is the way to go.
If you start trying to fill in the low spots with primer filler you will be waisting your time as well as a lot of money.
Making a body piece ( flow ) as I like to call it can take many hours, but the end result is well worth the effort.
Thick primer filler is a bad Idea.
First of all, primer filler wont fill anything that you can see with the naked eye or feel with your fingers.
Second A heavey filler wont take out much at all.
You need take your time and do it right, you will be so much happier in the end.