As someone who has driven, worked on, owned, operated, and now involved in sales of buses I would agree with both Nat and EastCoastCB that factory luggage compartments range from really good to really bad.
Crown and Gillig were considered the Cadillac and Lincoln of the bus business. Both companies used premium parts and pieces to put their buses together but even their luggage compartments leave something to be desired.
The vast majority of yellow buses leave the factory without luggage compartments. They are not cheap even from the factory--over $1,200.00 for a 34.8 cubic foot box on the driver's side and over $2,200.00 for a 47.92 cubic foot box on the curb side. Or almost $5,000.00 for a 137 cubic foot pass through under the floor luggage compartment. If you decide to put them on after the bus leaves the factory you will pay that much just for the boxes in addition to the cost of installation.
I would venture a guess that most of the very clever and handy people who visit this forum could put together compartments on their buses for a lot less $$$ than what the factory charges. And I would also venture a guess that they would be a lot more weather tight and able to carry greater weight than factory boxes.