I went with 1 and a half on the outside and 1 inch on the inside. That way it will wrap around the sides completely.
The foam was purchased from the same place I got my cloth from, yourautotrim.com.
I chose the high density foam:
1" X 54" X 108" 60lb. HD 54x108x1 60lb HD Foam.
I used the 3m spray adhesive to stick the padding to the boards
The cuts don’t have to be perfect, but it wouldn’t hurt. (it’s upside down)