Scott I just saw your posting so this might be too late. Here is how I did it last May after a lot of research (mainly on this forum).
First is photo of the original passenger seat foam. You can see how the springs were eating into the foam.
View attachment 3524769
To prevent this I used a material used for lining car trunks, Very durable and flexible. this is hog ringed to the metal border piece on the seat frame. You will also notice how I filled the spring coils with a dense foam for extra seat firmness.
View attachment 3524775
On top of the trunk liner I glued the new seat foam.
View attachment 3524776
To the seat foam I glued a denser foam apron to retain the seat shape on the edges.
View attachment 3524781
The new cover was then placed over this assembly and held in place with screws and beauty rings on the bottom.
View attachment 3524786
I am very please with the end result and love the comfort level of it.