I'm still of a mind for fiber-filled plastic resin molded hulls. The right plastic is extremely durable and strong, completely waterproof, and can be molded. Imagine a hull that has the windows already "cut out", snaps together, and is ready to sheet and accept internals within an hour after taking it out of the package. Kinda on the composite material idea: using a thin foam such as Dupron for sheeting. It would already be waterproof and only require sticking on the sides of the ship and painting to be battle ready.