At least on older models (00, 30, 50, 60 series), Bro-Tek has a pan that can stay on with the mower (though my mower driveshaft did sharpen up the edge of the trap door through the pan). I'd be willing to bet that if the 60-series version doesn't fit the 70 and 80 series (but it probably does) that Richard will have one to fit it soon.
The BXpanded one is larger and mounts using the mower lift. Obviously has to come off when adding the mower. And this one only goes on newer series (mine is a 30 and BXpanded does not fit it).