Slick and David,
I checked out the GS Dob info site and found that there are 2 different Tube diameters for the 8".
Model 200E - Length / Diameter: 113cm / 24cm
Model 200 - Metal tube - length 115cm - diameter 23cm
See here:
http://www.telescope-service.com/dob...iansstart.html
David will have to measure his to see which one it is.