I have no idea what I"m doing!! 
I got the 2017 riverside retro 181b, and just bought a 2019 toyota 4runner SR5. 
it comes ready to tow.
"Class III Towing Equipment -inc: Harness and Hitch"

so do idrive my tow vehicle to a camper store and tell them what type of rv i have and they will tell me and sell me which ball i need? 
Stephanie, RoamingArtworks
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That would be the best thing to do,,,,  You don't want to have the wrong size ball..  My 195 uses a 2 5/16"  ball..     You may be able to google the specs on your trailer.

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Hi Stephanie,

Congrats on your new truck!  Towing is one of those subjects that at first glance can appear arcane and mystical.....complete with Web Gurus and High Priests of the Internet, but actually it’s not so complicated. There are a lot of good posts on this forum about weight distributing hitches, anti-sway bars, electric brake controllers, proper electrical hookups, tongue weight etc. You’ll probably save headaches (and money) if you do some research before shopping for hardware. I bought my 181b from a reputable dealer and they correctly set up my hitch, sway bars and brakes without overcharging me (too badly).  Toyota publishes a 5000 lb tow capacity for your SUV and a loaded 181b will be over 4000 lbs.  You will want to be sure to get set up properly before towing at higher speeds or in the mountains. Good luck and keep us posted.... some of us are snowed in and enjoy seeing new posts!

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I have the same thing, and I took it to my RV dealer where I bought the trailer, they fitted a hitch and ball for me to make sure the trailer was as level as possible.  I have been traveling 4 years now and love it.  Make sure that your hitch is locked on to the ball because it can come off it not locked properly!  
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As  Peter suggested your trailer will be close to the capacity for your 4 Ruunner so it needs to be set up properly. Note that my 2014 4 Runner could not handle a weight distribution hitch set up because of the frame design. So I was limited to an anti sway bar that must be disconnected before backing the trailer. Also with the 4 Runner always have the shifter set to the left (manual) side and set it in 4th gear. Then it will act as an automatic but will never go into 5th gear. This might cost you a bit in gas mileage but will stop your transmission from constantly changing between 4th and 5th gears when pulling over flat terrain. When pulling up hill when set in the manual setting the transmission will automatically drop to the correct gear. When going down hill you will need to manually set the shifter to the proper gear to maintain the proper speed. I pull my 166 over some pretty gnarly mountain back roads and more than once have gone as low as 1st gear to avoid having to ride my brakes on a steep twisty downhill grade. If I were pulling a trailer as heavy as yours over the distances and mountain roads that I pull my trailer I would opt for a tow vehicle with a greater towing capacity. For short hauls and gentle terrain you will do fine with your 4 Runner.
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