Fishtailing.

I experience it too.  I even put as much weight as possible to the front of the camper to see if that would make a difference.  I'm left to believe that the weight of the spare on the back might add to the issues...but not sure as I've not taken the spare off to test it.  I usually have my fishtailing issues over 70mph especially if the road is a little jenky, like crowned or lots of patched areas.  

I usually have the fresh water full, but I do have some food and clothes stored under the rear bench.  I'll have to check to see how level the T@B is when towed.  It can't be off by much, because I have slept in it, etc. while still connected many times and don't feel like I'm leaning.  :-)

Fish tailing can be caused by your tongue weight being too light, relative to the total weight of the trailer. Loading the back of the trailer with too much heavy stuff behind the axle can create that situation. And higher speeds exacerbate sway.
If you weigh your tongue with a bathroom scale (or at a farm feed store etc) it should be at least 10% of the total weight of the trailer, or @ 15% max. A farm feed store can weigh the trailer, and separately the tongue, for you to do your figuring.

@Bill_Cochrane yep-2015 S Max Outback - empty weight 1860, tongue weight a little <180

The 2WD 4Runner has a 7300 towing capacity and we tow without a sway bar or equalizer hitch. We were a little light on tongue weight, but the Brahma wheel lock and Bal Leveler were at the trailer's axle.

The empty Dry weight is without propane tank, propane, battery and your "stuff". 

We've put about 10,000 miles on our Outback in ten months and the only time we experienced sway was when we put bikes on the rack and were in pretty heavy wind. We gradually slowed down, pulled over at the next interstate exit, and put the bikes inside the camper. We'll not do that again. Weight toward the back of the trailer is a bad idea. Good luck getting it figured out and please let us know how it goes.

We've traveled about 15,000 miles with our T@B which though it is not an Outback model, I do have the Yakima rack spare tire mount.   I tow with a Jeep Cherokee with a factory tow package.   Cruise is set at 62mph on a freeway, lower on two lane roads.   Never had a problem with fishtailing.

Smullis7 said:

I usually have the fresh water full, but I do have some food and clothes stored under the rear bench.  I'll have to check to see how level the T@B is when towed.  It can't be off by much, because I have slept in it, etc. while still connected many times and don't feel like I'm leaning.  :-)

You are looking at around 92# of extra weight if the freshwater tank is full and anything extra behind the axle and to the rear will also contribute to and create trailer sway.   Since the trailer is a higher profile, passing semi's does create a draft and crosswinds encountered after passing will create some instability when towing.   One of the keys as noted above by others is to add weight to the tongue since owners tend to store heavy items in the benches behind the axle to the rear and inside galleys of the clam shell units.   Not to mention that traveling faster than the rating for the tire (most are rated at 65 mph) creates heat build up on the tire sidewall and can result in a blow-out and a rollover accident.  

https://youtu.be/GfeyBxuIZOU?t=25

https://youtu.be/nd-hUX8memY?t=143

Yikes! That second one is a pretty on-point scary video Mike. It should be 'required reading' for all new trailer owners! We had a bit of a 'sway scare'  after first picking up our Tab - enough to take 'load distribution' seriously from then on.

I initially checked with our bathroom scale, and now I''ll 'lift' the tongue slightly, just enough to feel its weight (hopefully without blowing out my lower back ) ... I've become pretty good at guesstimating the tongue weight.

I assume that our load in the trailer has remained about the same, but there's that word "assume" again... I'll have to check the trailer weight again sometime.

Didn't I read somewhere that Tab recommended no sway bar? (BirdieJane, you forgot to resize that image before you posted it. - 6 megs! It took all my bandwidth!  )

So before buying and after we discussed sway bar vs none with Chris at LG and our dealer they suggested towing without. 10 minuets down the road the trailer was all over the place, filled our propane tank and still a problem. The hitch weight max for the Subaru Outback is 200 lbs. So we installed the sway bar 10000 miles later it has been great.

Bill, the recommendation is 10%-15%, I try to keep it at 10%, probably cuz that's what I learned way back when.
I think if you go over 15%, you're going to be lifting the front end of the TV  a bit, reducing traction and affecting steering response, at the very least.

I recently purchased a 2017 T@B S Max (Now the T@B 320 S).  We just took our first trip to Naples, FL from Bluffton, SC.  It is about an 8 hour drive.  I usually tow at no more than 65 mph.  I tow with a 2016 Honda Pilot FWD.  I found that the T@B towed very well without a sway bar, but when big trucks drove by I would get more sway, so just to be safe I am adding a sway bar to my T@B for highway driving.  This is my 4th small camper, I have had a Coleman Niagara Pop-Up, a Aliner Classsic, and an R-Pod 171 prior to recently purchasing this T@B S Max.  When traveling on the highways I feel it is better to be safe than sorry as you don't know how others are driving, etc.  A friction sway bar is not very expensive and just adds piece of mind to me and my family.  The main thing to remember is don't overload your TV or your trailer, keep things level, and keep your speed at around 65 mph or less and you will be fine.  Enjoy your T@B... we love ours !

Dockguy
2016 Honda Pilot -V6, FWD
2017 T@B S Max 

If you do get in to a severe sway situation that is really hard to control it is important to know that you do not steer in to the skid as you would to straighten out a vehicle that is fishtailing.You have to steer with the skid to correct a trailer fish tail. Scary as all get out because it goes against all your instincts and you need a lot of road to control the skid. I had this happen to me once and the only reason I knew what to do was because a friend of mine was with me and he coached me through it. Then we stopped and moved the car that was on the trailer 18" closer to the front. Problem solved. I think the spare tire up high on the Outback is a terrible idea. With our new TV I took the spare off our 2014 Max S T@B and mounted it inside even though we did not have any fishtailing problems.