Here is a real flight of fancy:
Rather than using a solid tube and if your metal working skills are upto it, make a truss tube with a dovetail mounting plate in the middle.
Doomsayer's beautiful scope which is described in his ATM thread shows what I mean, but where his truss ends at the position of the cassegrain primary, duplicate the anterior truss assembly to the back so the end product resembles a romboid shade with both pointy ends cut of.
http://www.iceinspace.com.au/forum/a...1&d=1243504704
The mounting plate would then sit below the central brace.
Very old school arrangement but visually striking.
Just a flight of fancy,
.
Mental.