The short answer is.. yes I can do this with my eyes closed. If you're not IT savvy it can be somewhat difficult. Rouge Wave is a total ripoff.
How would I do it? I would buy this. I currently use their UniFI Access Points in my house and I've used the Picostations for this exact purpose in the past. On my roof, with a 3ft antenna with wifi range almost a mile... until lightning took it out.
http://www.ubnt.com/airmax/picostationm/They sell for $80 bucks and are carrier grade. Mount it outside somewhere high and configure it as a wireless bridge. It's tiny. It connects to your marina hotspot and feeds internet down the cat5. From that point forward you either plug it directly to your laptop or you can plug it into the WAN port of a wireless router in your boat and then you'll have personal strong secure WIFI in your slip.
Now, to get way more advanced and what I'd REALLY do is, I'd buy the Picostation and reflash it with DD-WRT firmware. With that OS on the Picostation I can turn it into a wireless bridge and simultaneously turn it into a wireless hotspot with a different wireless name with a password locked down so only I know it. It becomes two devices in one. If you have a covered slip just mount it in your slip somewhere high and plug it in. Never worry about it again.