Per the 53' Merc advisor in the Early Ford V8 Club and my body parts book: The part number is BC 7654486 AA and the body parts book refers to it as "Container ***embly (top dust hood)". It was eventually made from the s****s from the tops. So the material would be Haartz Cloth. No pictures, diagrams or dimensions as of yet. No one seems to have seen one!
My 55 sunliner still has the original boot bag an it does look to be made of s**** vinyl,I can get dimensions and should be the same as your merc.
I will take some pictures of it but can not send any just yet as I need to figure out how on the laptop I am borrowing due to my computer biting the dust
I am sure you will get it figured out. What is the width, and length of the bag. What are the dimentions of the closing flap.
Mine looks to have started out as a 16 1/2x20 piece of vinyl,one edge of the 16 1/2 length was folded over and s***ched to make a smooth opening and then it folded in half and sewn togather making a pouch. It does not have a flap to cover up the opening and its possible every plant done it differently.