Cars that were originally rumble and converted to trunk might have the upper bumpers, they will not hurt (or help).
Aggressive weather stripping can cause fitting issues of the lid. What seems to work best is the universal "d" self stick attached to the inverted gutter on the lid, seals on the lip of the rain gutter when down, and still allows the rain gutter to function as a gutter.
Its fairly easy to seal the gutters up and add drain hoses, or add a dam across the floor to control water runoff.