Just keep in mind that wherever you place them, the weak link in that bulkhead/surface will now be the speaker cones/surrounds. They break down incredibly fast in the UV and then allow water intrusion. When I installed my new cockpit speakers last year, I couldn't find a single company that made speakers with optional covers. I now use a pair of small rubber dog frisbees to protect the speakers from UV degradation when not in use after a pair of Clarion marine cockpit speakers completely disintegrated in only 6 months.
Also, I would not expect a binacle to eliminate magnetic interference.