I have. I mounted mine there and I will give you the pros and cons and what you will find.
The bulkhead is glass over plywood. It is about 1/2 inch of wood sandwiched between two layers of glass.
The pros: I used to do a lot of camping on my boat and would raise my keel, anchor the boat stern to the beach and take a stern anchor and dig it into the sand. I could play the stereo and hear it while I played on the beach.
Here is the location I mounted them
The cons: That location puts the speakers in close proximity to anyone sitting near the bulkhead so that person has the music blasting in their ears while they block the sound from most everyone else.
Here you can see how close they are to anyone sitting near the bulkhead
My solution was to mount a new set of speakers at our feet in the center of the side walls of the cockpit seats. That allows for easy listening for everyone without blasting anyone's ears out and equal volume throughout. I didn't want to try and patch the old holes up so I left the old speakers in and wired in a fader between the old and new speakers. SO when I am at the beach, I fade them to the bulkhead mounted speakers and can hear the music. When I am sailing, I fade them to the new location.
I will try to get a pic of the new location in a day or so.
I hope that helps.