I use a volleyball kneepad. it slips over the whole lid and still shuts. A soccer shinpad would work also.

I've had a 1/4" layer of medium stiff foam with a dark gray leather cover installed in mine for 3 years. Just remove the triangular insert, cut the foam to fit and wrap the leather over it. Re-attach with the screws.

Both the foam and the leather can be found at Hobby Horse or equivalent.