it seems to have worked so far.
I ripped out the old beadin strip and all the old sealant to start with and then, this is the important bit, filled the bath right up with water to weigh it down as much as possible.
The rest was just lots and lots of sealant (out of a gun). I filled in the space between the bath and the tiles/wall with loads of the stuff, then I used a line of sealant along the back of both fins of the beading (just like the stuff you used), and once that was in place i also did a thin spread of sealant over the edges of the fins.
It seems to be working?