here is an Australian dealer for Carbon fibre Tube/rod/cloth/tape/epoxy etc etc
Here
Visual and Photography are two totally different beasts! just remember that.
as for expansion or Axial shortening/lengthening Steel has a lower COTE (Co-efficient of thermal expansion) than Aluminium and depending on the temperature differential you will get varying rates of contration.
To give you a idea ill loose a good 1 FWHM in the space of a hour in the first part of the evening after about midnight ill loose about .25 - .5 FWHM. and the difference in 1 FWHM is very noticeable when your CFZ or (Critical focus zone) is about 50 micron.
You shouldn't get much deflection over that distance but once again depends on how accurate you want it. if you want it strong and accurate for photography. spend the dollars make it right, look at Doomsayers efforts. done right
works very well!
If you triangulate the frame properly and minimize the slop in the connections you should end up with a good setup be sure to like i said enclose the OTA or Light will kill you, My canon 40d used to suffer light leak though the view finder and hence it got covered. My newt is open in the back end and hence it has what i call the shower cap on because light came past the primary and made its way to the imaging sensor (look at my website youll see my efforts for that).
If it was me ide be looking at a full tube for AP but its all about the weight sometimes and ill leave that upto you.
Brendan