Before coating *everything* in sawdust you may want to take a more analytical approach to identifying the stray paths which are causing loss of contrast.
Ideally all light hitting the first lens surface of your eye piece should have travelled sky->primary->secondary->lens. All other paths are stray and need to be eliminated/reduced.
An easy way to locate offending paths is (in a well lit room ) :
1. Remove eyepiece and position your eyeball where first surface would have been and look around (you may have to remove focuser to do this)
2. All surfaces you see which are not *in the secondary image* should 'appear' black, and if you can see 'sky' lengthen your tube. You may also see : Secondary edge and mount, spider, back of tube, inside of focuser.
3. Look at image in secondary mirror - All surfaces you see which are not *in the primary image* should 'appear' black, may include the lower section of the tube and primary cell, and ground edge of mirror and collimation dot.
4. Look at that portion of image in primary mirror - All surfaces you see which are not *sky* should 'appear' black, should only include back of spider and the secondary mirror (again) if the tube shows its too small or collimation is off.
5. The second image of the secondary will show the back of the focuser (should also appear black) and your 'beady' eyeball. Since this will be replaced you need not paint your eyeball black (;-)>
Note that to 'appear' black doen't necessarily mean it must be painted black. For instance the reflections from the lower section of tube in (3) are returned back along a 'glancing angle' and in this case a *smooth, gloss* surface offers less reflection than a roughened one. Of course the smooth surface will dump some light onto the primary but unless there is much dust on the mirror none of this light will find its way into the eyepiece (its too far off axis) (Light traps used to calibrate reflectometers use a maze of *glossy* black surfaces for this reason) Another way to avoid reflections is not to have a surface at all ! Hence the truss tube scope.
The relative contribution to your loss of contrast depends on the angular area as seen from the eyepiece and generally this means surfaces closer to the lens are worse offenders.
And so,IMHO, my recommendation is -
Extend tube or baffle to 'hide' focuser
Inside and back of Focuser } Black velvet for top of tube Opposite side of tube } or top cage
Edge of diagonal & other fiddly bits Matt black
Lower section of tube walls Smooth Glossy Black
Then again you may think this is going to too much trouble.
JohnH