Eddy wrote:

I'm planning to take off the ironware myself and fill up the holes, but
am wondering if there's something better to use than just the usual
silicone sealant?

It depends how much you want to pay. Sikaflex is much better than
silicone sealant for use when continuously immersed. It's also much more
expensive. If you want a compromise then MS-polymer sealants (modified
silicon co-polymer sealants) are extremely good for use when wet. They
are slightly less jelly-like than silicone and can be sanded and
overpainted (not relevant in your application).

Evostick Nail and Seal is an MS-polymer sealant. You can get it from
some branches of B&Q mainly the larger ones. Don't get confused by other
products with similar names.

http://www.amazon.co.uk/Evo-Stik-Nai.../dp/B0001P03SS
http://www.tool-up.co.uk/shop/diy/EVONAS.html

This is the cheapest supplier I could find:

http://www.pvrdirect.co.uk/productin...?catref=EVONAS