ATM Tube material - definitive advice please

["Clive Beale" <happysceptic@freeuk.com>]

I'm a newbie who has spent the last week trawling the ATM mailing list
archive (and Web) for advice on the best OTA material for my planned 6" f/8
Dobs.  I've now got to make a choice, but the subjectivity/personal opinion
(all construcive!) re this subject makes it difficult!  I've tried to sum up
the pros and cons - am I on the right track? Any contributions and
recommendations are welcome...

Aluminium
^^^^^^^^^
Pros: light; tracks ambient temp well; easy to work with.
Cons: rel. expensive?
Questions: What would be the min. recommended wall thickness for a  8" x
c.4ft tube?

PVC
^^^
Pros: rel. easy to get hold of; easy to work with;
Cons: heavy; rel. hard to paint (though I am told by a professional TM that
Hammerite paint chemically cures/bonds to PVC after a few weeks); may flex?;
bad thermal qulities?
Questions: 1) Would a 8"/4' tube flex enough (laterally - it would of course
need strengthening rings at each end) to cause problems? The same
(reputable) TM uses 3mm-walled PVC to build 'economy' Dobsonians.
2)How do 'schedule' gauges (US) convert to mm?  We don't use schedule in the
UK...

Sonotube/forming tube
^^^^^^^^^^^^^^^^^^^^^
Pros: cheap & cheerful; rel. light
Cons: need a lot of work to make waterproof/durable; harder to work with
(need to strengthen holes, ends, generally messy etc); hard to obtain (in
the UK).

So  - what do I buy?!!
Cheers,
Clive Beale, London, UK.