I have done it both ways, and have to say next time they go I will pull the dash again. It is so much easier. And you can see what you are doing to make sure they are secure and the the wires will all get tucked away. Behind the dash marine speakers arent too important. I went with regular Pioneer 3 way speakers over a year ago and they are fine. I am always topless, have been caught in some bad storms, and covered the ends of the dash in mud, no problems yet.
Complete rebuild axle/engine/everything swap in progress: Building stock width 44's with 302 from 01 Explorer. Motor has GT40p heads, Cobra Intake, and truck cam. Running A9L EEC IV stand alone engine from late 80's-90's Mustang GT. Big Bearing NP435 married to NP205.