When I built my roll bar I lost my over head speakers. My solution to adding a couple more speakers ended up being this Tuffy Dual Speaker box.
It arrived extremely well packaged, bagged, and in foam material. There was no way it could be harmed in shipping that's for sure. This mounts in front of the shifter, and will require you to drill four holes through the sheet metal. As mentioned in the instructions and on their website, the box does come with grade 8 bolts for mounting, and nylon lock nuts. Which is pretty impressive as many manufacturers these days give you the cheapest thing they can find. The torx bolts on the front are security bolts, but a wrench is included if you don't have one of these already.
The install really is quite simple. I used a silver sharpie to mark the four holes. Once drilled, simply bolt it down. They do include some gasket material, I however chose to use some silicone around the bolts and holes. Theres plenty of room under the Jeep to reach the nuts and get to everything, but you will need a helper. You will note in the picture above I chose not to use the screen they included for the speakers as well, however I am using marine grade speakers.
The only snag I ran into during the entire install was due to the speakers I chose. With their size and design they had to be spaced away from the front of the box by quite a bit. This meant they no longer fit in the box. Which resulted in me having to cut holes in the back of the box to gain the necessary clearance. In the end I made covers for these two holes, but you get the idea.
As for the sound, having the two extra speakers does help. I hooked those up as rear speakers, and I did fade the stereo to the "rear" some to balance the sound out some but it definitely made a difference.
Overall I'd definitely recommend this box. It's an easy way to add a couple 5 1/4s to a YJ. Obviously the ideal way to add speakers would be an overhead bar, but this doesn't work for some of us due to roll cage issues or other reasons. For me this was my best option, and turned out to be a solid purchase.