I wanted to make a "light cargo tug" for the Federation to use in A Call To Arms Star Fleet. The Ptolemy class tugs would be a different class to this vessel and capable of utilising battle pods which turn them into a light cruisers. This ship however would be a support vessel capable of cargo and troop transport and lightly armed by comparison unable to attach a battle pod.
Looking around the available miniatures, I decided to hack up an Federation Command Cruiser from Amarillo Design Bureaus' 2400 series (i.e. 1:3788 scale). You can find the miniature here.
I kept part of the secondary hull and attached a rare earth magnet to the back of the hull which I had cut and filed to shape. I also removed the sail from the secondary hull and attached the primary hull / saucer section directly to the secondary hull. It was a hack job, but it did turn out to work pretty much the way I wanted it to. My big mistake was removing the deflector dish and so had to paint one on after stuffing up that area of the secondary hull.
The cargo container section came from a Studio Bergstrom / Irrational Designs cargo hauler (you can find that miniature here). I have two of these and the first model had the cargo section made of resin (the other is metal). As it was resin it was light weight enough to easily attach to the tug with a second rare earth magnet. Each of these being a 1mm x 1mm round magnet.
So there you go. One Federation light tug.