Potting Compound

[David L. Jones]

Anyone know of any cheap and readily available potting compound, or
something that will do a similar job?
I used to work for a company where this stuff was literally on-tap, so
never had to source it myself for home use until now.
I know Farnell have a whole range, but it can be expensive, and not
convenient and quick to get (e.g. this weekend).
Jaycar and Altronics have potting boxes, but no potting compound by
the looks of it.
This is for an underwater app.

Any solutions from the like of Bunnings perhaps?

I've used hot-melt glue on occasion for quick'n'dirty jobs like this,
but not for underwater apps, where I suspect it's not going to be any
good.

Thanks
Dave.