If you're looking for something to grab a weak wireless signal, you can use a USB wifi antenna. I have a few of these and they work great:
http://www.amazon.com/Rosewill-External-Antenna-Wireless-RNX-N180UBE/dp/B004BV4JXI/ref=sr_1_1?s=electronics&ie=UTF8&qid=1428901489&sr=1-1&keywords=rosewill+180
They're around $20.
Tips on positioning your antenna: Imagine putting a donut around your finger. In this example, your finger is the antenna, and the donut is the region for best transmitting/receiving. The best region moves out perpendicular to the antenna in an expanding donut shape for this type of antenna. This means that if you point your finger (antenna) at the RV park's wireless router, you'll get terrible reception. Also keep in mind that wireless signals can't travel through the metal exterior of your RV, so put your antenna next to a window or even run the usb wire of the antenna outside of the RV if you can. You can buy USB extention cords but I wouldn't have more than 5-7 feet in length from the usb port on your computer to the antenna since the longer the cord length, the slower the connection will be.
One more tip. Let's say you have this antenna next to the window on the inside of the RV. If you put something metal, like a sheet of aluminum foil or even a coke can that's been cut open, 1.5 to 3 inches behind the antenna it will result in a greater range out the window. Google "coke can antenna" to see some examples and pics.