After reading a LOT of stuff about different types of touring bikes, I decided on a MTB to tow a two-wheel trailer. I bought a steel frame/fork on ebay and built it up. It is a Dirt Research brand using Columbus DR tubing (supposed to be a step up from entry-level tubing). I originally used XTR Linear pull brakes f/r, but have switched to a 29er disc fork for greater stopping power, with less chance of overheating rim/tire on long downgrades. I have it geared low (22/35/48 front, 11-34 rear) for extra spin up hills. Planet Bike fenders for 'dryness', Randonneur bars with road shift/brake levers, and a 'surgically altered' Brooks saddle.
I built my own low center of gravity trailer, and it has proven to be quite pleasant to tow. On a winter trip to Death valley, I was able to HAUL downhill at 40mph carrying about 30lbs of gear without any wiggles, wobbles, or other concerns for health or safety!