On a 13 footer, two key decisions to make:
1. Bathroom or no bathroom? To get a bathroom in a trailer this small you have to give up a lot, and the trailer will be heavier. Too much IMHO.
2. AC or no AC? The older vintage units were not designed for roof air, so its difficult to add AC later.
You're off to a great start already. You know what you don't like about the popup, and you know what you like about your friend's
Scamp.
And Scamps tend to be more available, particularly in the small size, than any other brand out there.
As far as winterizing, even your popup, if it has a sink, will need winterizing and needs to be stored when not in use. Winterizing a basic
Scamp 13 with no toilet or bathroom is about the same amount of effort as winterizing a popup.
I have a 1977
Trillium, and winterizing it was easy. Winterizing my
Escape 19 was a lot more work, still not a huge job. Took me 1 1/2 hours to do the
Escape. Each appliance/connection that involves water means another thing to winterize. Toilet? Hot water heater? Sink? Shower? Fresh water tank? Gray and black water tanks? And all the plumbing pipes as well.
Regardless of what you own, I am a big proponent of keeping your camper under roof when it is not in use. In my area, a simple carport works just fine.
Four season trailers in such a small size, I am not aware of one currently being made. Four season trailers tend to be a lot heavier, more than your Outback can handle, and double or triple the cost. Maybe someone else knows of a good four season,
light weight and compact molded trailer.
One thing we learned after buying our first molded FG trailer is we wanted a permanent bed AND a place to sit. A permanent bed allows you to customize a mattress to your liking, instead of trying to sleep on a patchwork of dinette cushions. My back does not like sleeping on dinette cushions.... A foam bed of your liking, plus an old electric knife, and you can custom cut a mattress to fit in your camper. Or use an air mattress! For some reason, my back likes an air mattress just fine.
The trailer we bought had the former, but not the latter. Oops!
Sold that trailer and got our
Escape. On a 13 footer, without a bath they most commonly have a front gaucho (couch) that converts to bunkbeds. This gives you a place to sit! Sure, most of your time camping will be spent outside, but when the weather is foul, its good to have an inside place to sit. If you can possibly do without a bathroom, it really makes a 13 footer more usable.