Stuart,
It is irritating that seatbelts get stuck.
On a 2 seater the tonneau cover needs to be folded in specific way, to prevent interference with the seat belt. I am sure ther are posts with pictures on how to do this. Can this be adapted for the 4 str, I wonder, or is the ditance too large? Perhaps a trick with a rod that supports the tonneau?
Good Luck,
Bert