You can get spray on silicone, they use it down here to spray the tops of power poles so they dont catch on fire during the summer
Otherwise a quick coat of kill rust, then in the corrugated bits you fill with insulation, and use some weather board/plaster board to hold it all in. Add a roof slope, to allow water to drain off(into a tank i guess), and it's all set. Ideally the roof slope would be insulated underneath, and it should must definitely be water tight. Might be expensive to paint a 40' container