ruthiebaby,
We have a 21' hard sided travel trailer. It was rated as a four season trailer....for whatever that means.
We bought it mainly to use in the Fall, Winter, and Spring months for hiking, canoeing, skiing and snowshoeing trips. In the summer, we are more often sleeping in a tent....or under the stars .... on rafting trips.
Towing a trailer in the winter isn't as bad as you might think. Look around you will see lots of trailers, from snowmobile trailers to trucks. Just take it slow and use common sense. And the neat thing is that if gets too bad (or you just want an excuse), you can pull over and wait it out in style (think hot chocolate and popcorn) while the folks in Subaru's are stressed out looking for a place to pee.
Anyway, that's my take on it. You are getting lots of great suggestions and I am sure you will come up with what's best for you.
Steve