That is about the best.

One other solution suggests itself, and that is to fill the bilge
keels with a substance that would prevent water rising up through
them. However, given that the state of the interior surface is
unknown, it is difficult to think of a substance that would do the
job.

An off-beat possibility would be a substance viscous enough not to
penetrate the hull and lighter than water, so that it would float on
top of leaking water and thus form a water-tight seal.

Do you think either of these ideas are realistic?