I'd really like to have a hot tub sunk into the deck.

One of the main requirements will be to insulate the tub

Seems like an ideal project for expanding PU foam.

My brother's fibreglass tub was delivered fully plumbed and open framed
which showed 200mm or so sprayed on the outside. It appeared to be the last
job they did as it was covering the pipework, lights, and pump brackets in
many places. Cover panels are fitted on site after the hook up and mounting
has been completed, maintenance is via these panels.

The spec meant the deck had to be lowered in that area so the tub could be
ground supported, the bonus was it gave it more privacy and cosiness to the
installation.

Probably the first Japanese hot tub built in this country was built by
a bloke I know who was in the Korean war (and presumably spent most of
the war in a hot tub) He used a stainless steel milk container, bought
cheap at some farm disposal sale. Its a very good hot tub (speaking
from experience here) and since then he has built several more the
same way for other friends

Anna
~~ Anna Kettle, Suffolk, England
|""""| ~ Plaster conservation and lime plaster repair
/ ^^ \ // Freehand modelling in lime: overmantels, pargeting etc
|____| www.kettlenet.co.uk 01359 230642