[folivier]

The easiest and cheapest way is to get a directional antenna that connects to your macbook. I think Clarke uses one, not sure what brands are best. Other option would be to get something like a WifiRanger Go that has an antenna. We have a WifiRanger Go which works pretty good but we seldom use campground wifi and instead use our Millenicom mifi291 with a Wilson Sleek booster. That works on Verizon and has a 20Gb/month limit.