One reason steel ships don't rust away to nothing is because they have sacrificial anodes applied around the hull. Removing the old anode, probably totally disintegrated, would slow the rust, but once started, it could be over soon. Unscrewing the old anode is the tough part...they don't cost much. If you don't have enough height to install a standard one, they make them with segments so they can be bent so you have room to install. An impact wrench really helps getting them out, but you may be able to do it with a socket with a long cheater bar. if yo uhave to pay someone to do this, it wouldn't be too cost effective, as there's no guarantee it would have been done in time...there may be too much damage already. If you replace the anode rod periodically, the tank should last longer for not much cost.
