Would a storm door closer work for your rod locker? The kind with a push button door lock. That'd be a low cost solution to keeping it open when you wanted, and a cool anti-slam mechanism! I can't really tell if that would fit the application from my point of view, but it crossed my mind!
Also, I don't know what your budget is, but I was pleasantly surprised when I went shopping for a sound system for my boat. If you have an Autozone in your neck of the woods, check it out! I managed to pick up a Kenwood CD player with a built in 200 watt amp and two speakers for less than $100 bucks. I'm not very tech savvy, but the thing also links up to phones and various other gadgets. (My kids do that) I have to admit, the darn thing sounds pretty good!
That might just be the ticket!!!!