OK, I have the new tow bike, a 2010 Charge Mixer 8...
The new Mixer with the venerable Cannondale.
My old Cannondale will be retired from towing duty, and be come my ride bike, the Mixer 8 will become the workhorse.
The Mixer 8 is a steel framed bike, Tange Prestige Double Butted tubing, Shimano hydraulic disk brakes (man they stop time!) and an Alfine 8 speed hub, should be very little maintenance on this bike

The wheels are 700C with 36 spokes, so they too should hold up, and I put some larger Schwalbe Marathon Plus 35 tires on it, for a bit more volume, they just fit.
On to the new hitch.....
On the Cannondale I had the hitch attached to the seatpost, this worked, but I have always been concerned of the potential damage I could do the the frame with the back and forth leverage from the seatpost attaching point.

That is a close up of the existing hitch.

A 165lb delivery
Below is a quick mock up using some wood to give an idea of how I want to attach the new hitch, the size of the plates, the gussets and the hitch are will change, this is just a crude mock up, but I think you get where I'm going.....
I'm looking for some comments, if you see something that sends up red flags, please do tell, I'm not married to this exact design, so I am looking for ideas.
I will also say that I've looked hard at the hitch down at the axle and I find it not to be so good, I understand that with a fairly heavy load, which I will carry daily, the trailer usually does not track well, and turning in one direction is easier than the other etc.
Comments please!