Have you tried just using a 10' USB extension cable and a USB Device? I think I'd try that first.

If you get one of these, get one which is rated for the highest protocol -- not because the marinas will have these (yet), but because the internal antenna that goes with those little USB units is better. I bought a Linksys unit which I use because when I am trying to use my office's VPN network. The Port Networks "bridge" that I have doesn't have the troughput (but I think the Port Networks unit is somewhat somewhat better, if not fast enough.)

In most cases you can keep the unit in the cabin; however, if you need to route it outside, I have found that if you are concerned with the "rain", you can take a ziplock bag and put it over the USB wi-fi antenna.

We bought a Port Networks unit years ago, it does work as advertised, it's just not "fast" enough. Right now I'm on a Verizon Mi-Fi card which is recieving a signal inside the boat.