In that case, I kind of think that a lot of the Skirmish ships would likely be modified forms of cargo vessels. You'll likely not find a single vessel that isn't armed, the skies aren't friendly in the slightest with piracy and raiders rampant. I think that the mainstay of trasport might be something akin to the Goldfish.
The Goldie has plenty of below-decks space for at least light cargo, and if you were to remove the front weapon you'd have a little bit more on the main deck, as the engineering house behind that big boiler would offer manueverability for the engineers. You'd certainly keep those side guns to fend off raiders, and the Goldfish is reliable enough and quick enough that I might rate it as a light, independant freighter.
Now, as for a heavy freigher, we're getting somewhere. For a heavy freighter, I'd probably go back to the Junker, just modified very, very heavily. That large balloon would be pretty cheap, and necessary for carrying cargo and freight to and from ports. Again, armed, as pirates would be likely. I think the Magnate also deserves a mention here too, as the Magnate practically IS a freighter. That's not a warship, and I don't even pretend it to be. Her hull is too fragile, her weapons too dedicated to fighting from her flanks, and that below-deck space would be perfect for goods. Slow, of course, but the Magnate would rate a heavy freighter, no question.
As for personell transports... Well, you've got the Boss Ships. Those are practically flying cities, honestly, and you'd be able to carry any statesman in a ship even lightly designed after them.