Was just looking at the ship your adding and was thinking three or five railcraft tanks inside to hold the oil would end up looking like the real oil tanker storage that has oil stored in several seperate bulkheads. Could always cheat a bit and pump some oil from another oil source to half or three quarter fill them. These tanks also have valves and can be joined to make one large storage tank by using BC pipes across the deck of the ship. Real life oil tankers have quite a bit of pipe work on deck for equalising tanks etc. Also, railcraft tanks can be dyed to whatever colour you wish. Well at least the steel ones can. Not sure about the iron ones. I tend to only use the steel tanks as they hold more per block. If your not familliar with these tanks they can also have glass viewing sides.