How to Solve Multiple Waves on '70 Rear Deck Filler Panel?
 

A fellow who used to do some welding for me has since retired. He put new rear quarters and filler panel on the car and I was about to epoxy prime and couldn't believe the waves on the filler panel.

There are 4-5 large low spots that cover all but the drivers side last 8 to 10 inches.
I filled with filler and sanded down to the high spots but have no idea how to transition that far to the good section. I could float the entire panel but then how to transition to the ends. What to do on the sides is also doubtful. I ran a DA down the long edges - vertically - with no back glass in.

I'm out of my area of knowledge by a long ways and haven't had luck searching as just get welding suggestions on it. Thanks!

Would love to see a photo. Is this a Bonneville? Sounds like a big car.
How wide are the low spots? How long? I assume this panel is welded in?
I have done these on first Gen F body cars and a GTO..

"70 GTO HO 455. The only thing I can take pictures of now is the different high spots that I've sanded back down to.

Had about 4 waves with each being 3-4 inches wide. Usually I miss these things until the primer is on but caught this one.

Since I can't see the piece without the window, I recommend using a 12-14" long rigid board file ( Sanding block that takes a roll of sticky back paper. Sand with an " X" pattern all the way across, do not sand end up end.
I use a contour DSB system from Eastwood and it comes with hose to hook it to your shop vac.