Looking for a Strong sub grill

My sub (12") is mounted in an area that routinely has something laying on it - its in the spare tire well in the back of a wagon. There is carpet over the area - and a rubber mat, but I need something in the form of a grill that is strong enough to support anything laying there (nothing like a cement block, but sometimes a box weighing up to 75lbs.). I had thought about a thicker steel mesh - any ideas or sources? Subtlety is EVERYTHING.

Holy smokes.....thems serious grills. I need thse on the front of the car.....heh heh. Might try the mesh - do they even sell it THICK? Everything is flat in this area so it will have to be flush. The hinged "lid" that covers the spare tire well is actually made of 3/4" plywood so anything is possible. I was also considering recessing the sub the full 3/4" from the surface and then putting bars across it like a grate...then a standard HD mesh grill for looks. Subtlety is EVERYTHING.