There are quite a few S13 owners towing with Outbacks in the “Scamp Travel Trailers” Facebook group. It’s a very active group, and you’ll likely get a lot more feedback.
No personal experience, but general consensus over there is it will work but it won’t be speedy going up long western mountain grades. Stopping periodically to allow the transmission to cool down would probably help. (Pre-2020 Outbacks used to have a caveat to that effect in the manual.)
The actual loaded
weight of your trailer along with the total payload you’ll be carrying in the vehicle- people and gear- make a difference. Tow ratings are based on two adults and nothing else in or on the vehicle.
Elevation is the biggest difference between eastern and western mountains, Gasoline engines lose 3-4% of output for every 1000’ above sea level.