According to Trailer Life's 2001 towing guide a 2001 Forrester has a 2,000 lb tow rating. I towed my 2006 Aliner LXE (1,700lbs fully loaded) with my 06 Chevy Cobalt 2.4l for well over 40,000 miles, and it only has a 1,000 lb manufacturer's suggested towing capacity. I recommend installing a transmission cooler (if you have an auto) and installing an electric brake controller and getting a trailer with electric brakes, whatever the weight. Some of the Aliner clones are not built like an Aliner so they are very heavy. Be sure to get the actual weight, not just the sticker weight inside, as they can be off by 500 lbs if you have every option under the sun like my LXE had.
Chip