On Sat, 27 Jul 2013 14:27:01 +0100, mark wrote:

The problem is that when tightening the waste fittings the two skins of
the bath move towards each other and likely to break if tightenened
enough to make a seal. The gap between the skins is about 15mm.

Make hole in outer skin bigger so the waste fitting only needs to
clamp on the inner skin. You might be able to get away with just a
couple of slots opposite each other to slip the fixing nut through
then drop the waste in.

If you fill the gap and you get a leak between the waste and inner
skin but not between the waste and outer sking the gap between the
skins will fill up with bath water... That'll be really ripe after a
few months years...

I think you'd have a job ensuring a perfect seal all the way round
between the skins.

--
Cheers
Dave.