I finally managed to get the Akita from SH4 in with proper textures. However, because the texture has to be embedded directly in the file there can only be one skin per merchant ship model.
It also doesn't help that there are still weird issues (the ship's stern is too low in the water for no apparent reason) and that I'm unhappy with DRM, crew ghosting through bulkheads, bad dialogue, bad camera angles, etc etc etc.
All in all, this has left a bad taste in my mouth. I could go into more detail about how frustrating these SH5 "improvements" are, but I guess I'll get back to modeling & skinning for the next Merchant Fleet Mod version.