There are solutions out there to boost the signal.
A wifi repeater wont help you much because first off - the off the shelf boxes dont come with powerfull antennas and then when you throw in the fact that a repeater has split its bandwidth in half you end up with a unstable slow connection.
What you need is an antenna, an ubiquit airbullet, and your own router.
For an RV park I would recommend a small grid antenna which wil only requre mild aiming at the internet soure.
So you would have a pole or something to mount antenna to on rv.
Antenna connects directly to airbullet, ethernet cable from airbullet directly to router, then you can use router for wifi in RV.
Since you are going from campground to campgroud each time you will need...