Originally Posted by AlanT
I am not certain, but I think that my corner cushions in a banquette have no solid back, just the foam. I will check later this week when I'm on the boat and revert.
Originally Posted by Soo-Valley
Use 1/8 veneer X 4 to get 1/2 inch. Build a frame into the corner for backing to bend the 1/8 material past the point where later you will later cut it. Apply glue and lay the next 1/8 and so on. oversize so you can trim to suit.
These were my initial thoughts.
Regardless of which you choose its best to cut the foam about a 1/2" oversize around all sides compared to what you'd like as finished dimensions. Make the cover the finished size desired and "stuff" the foam in to fill the shape w/o any puckers.
If stuffing is difficult use of a very light wt plastic bag (dry cleaner bag) will help and can be left in place or pulled out after providing opening left toward the far end from the covering opening.
Good luck & let us know how it turns out.