There are many "Antennas" but in truth I do not recommend an antenna, I recommend an active electronic device... I use what I call a "Wi-Fi Modem" specifically a Linksys WGA-54G Wireless Game Adapter.. No longer made but read on.
This device acts like a common Cable Modem, but instead of looking to a Cable for the Internet, it looks to the park's wi-fi (Which then goes to cable here)
However it's old and cranky.. but then so am I so we get along.
I also have a nice little thing about 1/3 the size of a pack of coffin nails (Ciggearatres) called a TP link Mine is the model TL-MR3040 and I suspect it too is no more but other models are still out there.
This device can do all the following
If connected to a Cable Modem.. it is a Wireless Router
If connected to a wireless router, It is a "Modem" like my WGA-54G
And it is a repeater (And it is in that mode as I type feeding two other devices on the table, this one is hooked up via the WGA)
So it can replace the WGA and allow a device without Wi-Fi to connect Wireless
It can Replace a wireless router
OH, and there is a USB port on it, I have not attempted but as I recall if I stick a Cellular USB dongle in it.. It's lets me use it across my net.
all in all it's an amazing box of electronics
Now, what I recommend for RV use.. There are several devices, one is the Wi-Fi Ranger
This is a 2 part (or 3) system
1: Ye-old power supply (Wall wart or brick)
2: Router: this goes INSIDE your RV. it allows you to connect multiple devices including a wireless printer and to share files and printers across your LOCAL area net (LAN) same as I do here same as I did at home. Same as most families do.
3: Outdoor module This is once again a "Wireless Adapter" like my WGA but newer and faster and more reliable, Power for the outdoor module is carried from the indoor unit on a CAT-5 Cable (Standard "internet" modular cable)
There are a few competitors now to Wi-Fi Ranger and I can not, yet, recommend one over the other, but this is the class of product I recommend.
Wi-Fi Ranger corporate siteTP link corporate siteOh, my TP link, got it on Closeout for 13 bucks,, of course that was last year so it's all gone now, but they have others, more expensive (Should have gotten 2 of 'em to be honest).
Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times