Ok so I have my commuter (Marin Mill Valley see photo below) and it is all AL (both frame and fork). I like the bike but I do put a lot of miles on it as it sees both commuting and family use so I would like something smoother...ok what I am saying here is I want steel.

My problem is my need for a sloping top tube because of the trailerbike I use with my son. If I get a traditional geometry frame there isn't enough seatpost to stick the trailer hitch onto, but I can't seem to find a steel frame with sloping geometry that both fits and takes a 700c wheel and say 32mm wide tires. I was thinking Surly Karate Monkey but the top tube measurement seems SOOO long, am I missing something there? I guess if I was doing custom It would have the same dimensions as my Marin but be made of steel....and if I was adding to the wish list I would throw disc brake tabs on there too.

Does the bike I am looking for exist stock or should I just go custom? Or should I just suck it up and get a MTB and ride the 26" wheels with slicks?