I just did a system for my friend with all Memphis audio stuff.
Marine 5 channel amp (The Memphis Belle 600)
I ran 2 sets of cabin speakers off the front channels
and the tower speakers off the rear channels
The sub channel for a Memphis M3 12" in a ported box
Amp - $700
3 sets of Memphis marine Coaxials 6.5" (140.00 per pair)
12" M3 Sub $250
The only thiing not marine was the sub but it will be fine it is in a dry place.
This sytem bumps and gets loud. The Marine Speakers get real nice sound for not that much. The reason you don't see memphis in any catelogues or websires is becasue you have to buy from an Authorized store dealer. Wihtout tax the system was 1250. I know that is alot to drop at once but take it from me. I have tried to poece sytems together month by month and never have been satisfied. This stuff is great gear and doesn't cost as much as big name brands. As far as a deck I would go with one of the Clarion XMD models. Those things take tons of water a still work. You dont have to hide it in the glove box becasue the face is waterproff. Also you can have two remotes one for the driver and one on the ski deck. Those head units can be high but they are woth it. You can get a factory reconditioned one at www.bass-entertainment.com
Hope that helped. If you want to know more just email me www.memphiscaraudio.com