The "Expander", a cargo hull filled with engines and support, turned out to be very useful. In addition to constructors and colony ships I was even using them to get my trade routes laid down faster in the Dreadlord scenario game with the huge map.
Thanks, y'all!
Cargo hulls also dramatically reduces the tech requirements for a viable anti-Dreadlord interceptor (speed 11 or better, attack of 1 or better, whatever support is needed, and maybe a scanner -- or the Eye, what a Wonder!) In that next-to-last Dreadlord scenario I kept asking myself, "When can I finally build my interceptors?" I realized I needed like Warp MkIII engines to really have a go at it, and in the previous scenario I had 7 planets and a bunch of allied AI's with powerful economies helping me tech up.
With the "Privateer" armed cargo hull I think I was intercepting Dreadlord non-combat shipping at like Impulse III. I don't remember exactly, but it was way before Warp III. I built them as a temporary stopgap when the Dreadlords showed up until I could build "real" interceptors, but against unarmed ships a cargo hull with a pea shooter and one hitpoint might as well be a fleet of battleships.
Cargo hulls make excellent scouts, too. A big box that's all engines and scanners is way better than the plodding, half-blind stock scout model and not very expensive, especially on a parsecs-scanned-per-turn / cost ratio.
Anyone made a survey ship out of a cargo hauler yet? Do hitpoint anomaly upgrades work on them?