To realistically keep these tanks in good condition it would need a long treatment time once raised they would need to be completely immersed in a pool of salt water at the same salinity as their current environment then slowly, very slowly reduce the salininty until the water is purely fresh water, then there are some special chemicals you can start to add to try and reduce the active rust. Eventually you may be able to stabilise it enough, blast it, and then paint it with rust prohibative paint, or you may wish to completely take the vehicle apart and restore it to a running order, but you'll need to coat every surface to stop it rusting.
