Hi, I just use small speakers that come in enclosures and just sit then the back deck secured with velcro. If I am slow in traffic they are fine. At speed with the top down, not good. But with the top up, fine. You can move them about if you have luggage. And doesn't require any mods to the car.
MarkB
If you want pictures, send me an email address. I'm not smart enough to post one here.