Another factor with a Yagi, particularly the ones that look like UHF antenna is that they only have about a 15 degree arc to aim them. With the right setup you can actually pickup a signal as far as 5 miles away. The problem with that is you would need a rifle scope to aim it that far away.
Directional antenna's like Yagi are meant to increase your distance, not really to give you a stronger signal at short range. I have never seen a campground that requires a Yaga to pickup the signal within the park (although some may exist). The biggest issues you will find with campground WIFI are:
1) slow/overloaded internet connection- no WIFI antenna will fix that
2) bad WIFI network design- using too many repeaters, the only way a WIFI antenna would fix that is if you could figure out and connect to an access point closer to the main building
3) your trailer is a big Faraday cage (aka cone of silence for WIFI)- this is where your WIFI antenna is a big win, getting it near a window or better on the roof or TV antenna has the best chance of improving things. In this case an 8db Omni with a short good quality cable (5-10ft) is more than enough.
Rob
rvtechwithrvrob.com