Got around to putting some rear speakers on my 2007 SX230.
I had my mind set on putting them behind the rear facing seat backs.
First step was getting the seat backs off. This ended up being the most time consuming part of the project. Each seat back has 11 bolts. The side walls inside the engine compartment block 6 of those screws on each side. Getting those side walls off was a chore. There are only 4 screws at the bottom of each wall. You only need to drop them down enough to reach the bolts, no need to take them all the way out. There is one bolt on each seat that requires to basically lay on top of the engines to get to it. The starboard wall has a blower mounted to it and will be need to be removed. After all that, the cushions came off will relative ease.
Next, I marked and cut the holes for the speakers. I ended up using one of the blower/vent holes on each side for the speaker location, widening the holes to fit the speakers. I then just added another hole lower to mount the blower and vent.
Next I mounted the speakers. I through-bolted them with stainless hardware. I got some rear speaker covers that just add some piece of mind to protect the speakers and make it look cleaner inside the engine compartment.
Next was wiring. I was able to thread the wires through the starboard side easily. At the head unit, I added a DPDT switch so that I could switch between the inside rear and outside rear speakers (main use will be while swimming behind the boat). This also prevents under powering the speakers If I were to wire them in series.
After wiring and checking sound, it was time to put the boat back together. The seat backs go back on pretty easy, take care not to scratch the boat with the bolts. Then, getting the nuts back on, careful not to drop any nuts or washers. Now those dang side walls. They are big, awkward and snugly fit. They will require contortion, beating and cursing. But, once you've got them back on, you're pretty much done!
There is a great sound difference, 100% better from behind the boat, which use to require a very high volume to hear it out in the water. Sucked for anyone sitting in the boat.