Congratulations on your new Scamp!!
Beware tongue
weight. Your tow rating (2700#) is plenty for a 13’er, but the tongue
weight rating (200#) is marginal. You’ll want to skip the dual LP tank option.
Not sure about a transmission cooler for a CVT. Check with your mechanic, or perhaps other owners of late-model Subarus will chime in.
I’d always go with a wired proportional controller if possible. I think your 2016 should accept a wired set-up. The Tekonsha P2 is a popular choice.
The 13’
Scamp is naturally stable, so a sway bar shouldn’t be needed for normal driving conditions. However, having one adds an extra measure of safety in an unusual situation, like a sudden gust of wind from the side or an emergency lane change. Your call.
Most important thing to avoid sway is proper
weight distribution. Carry heavy stuff over the
axle and toward the front to maintain a minimum 10% tongue weight. Too much weight at the back is the most common cause of sway. Make sure your ball mount allows the trailer to sit level or slightly nose down.
You may also need towing mirror extensions, since your Outback is narrower than the
Scamp. Some Outback owners use them; others manage without.