Wow, thanks for all the information and advice.
We will be loaded with gear, but will be mostly on minimally hilly southern highways and taking our time.
Even so, with our research and your comments, we were tending in the "bite the bullet" direction until we found a website for sylvansportgo travel tent trailer. It is only 840 lb and was reviewed by someone who used it with a mini-cooper.
Are we crazy to be pushing our 2000 Legacy with 200,000 miles to do something like this? The above trailer is spendy but the lightweight seemed good and made us think it might work afterall.