I have some of those! They are reserved for making my Accord top-heavy!
I used up the rest of the fanfold foamboards today. One panel between each set of studs before the shelves in back and then I cut up the last board to fill in the bottom, but ran out.
I will use the scraps to fill in gaps where the boards were a little too short.
I think that I need about fifteen more to insulate the area around the shelves in back.