So yeah, I've unwrapped the bottom of the hull and slapped a quick placeholder texture on it for now. I'm still undecided about whether to go with the white/red colours or the more rusted orange/blue of the SS America, so that's something to experiment with in the future.
I originally unwrapped the hull in such a way that it would use a tiling texture at a 1x2 ratio, like a 1024x2048 texture. The texture tiled horizontally, not vertically. However this allowed for virtually no unique elements, it had to be uniform to avoid artefacts. So here I tried unwrapping the ship fully onto a 2x1 sheet (it's currently 4096x2048 but it'll probably be knocked down from that). This allows for fully unique detailing, but it's not very efficient and requires it's own, high resolution sheet.
I'm still debating which method (tiling or unique texture sheet) to use for the hull, so I'll carry on experimenting with it.