Pop Pkg 2 is Ext Auto dimming, Rear Bumper Cover, Cargo Tray, All weather liners, and splash guards. It doesn't have crossbars on it, those are a stand alone accessory (that we can't order with new ones right now).
And I don't know what the difference is in the car itself is, but the Base Model is only rated for 2,000 lbs while the Premium and above are rated for 5,000 lbs. That probably has something to do with the trailer assist package that's only on the higher trim levels, but I can neither confirm or deny that at this point. Note also that for towing ANYTHING more than 1,500 pounds, Subaru recommends trailer brakes.
From personal experience, when I was towing my 12' cargo hauler with my pickup and hit a pothole, destroying the tire, making the trailer hit the ground, and then bending the axle, it's a VERY scary thing to have happen, even WITH trailer brakes. (I ended up having to call a wrecker to have my trailer towed in, even though I had a spare and an actual small floor jack, due to the damage to the axle.)