Eric,
Measure the width of the freestar carefully! my windstar will is JUST
wide enough for a 48" wide sheet, no extra room on the sides. I'm not
kidding, you wont have any room for carpeting on the sides. You might
fit a thin plastic sheet, but you'll have to hold it up out of the way.

As a side note, that same narrow spot is exactly where the 3rd row
seatbelts anchor into the floor...that sort of padding, isn't it?
Anyway, the sheetgoods fit between the belts at that point, but you
aren't going to get anything else between the sheet stock and the
seatbelt except the plastic sheet as above.

A freestar may be different. Take a tape to the dealers and insist they
take the two back rows out, then measure.

John