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As I understand it key issues are:
1. Paying attention to baffling opposite the focuser and around the primary mirror.
2. Avoidance of heat plumes (usually from the observers body) through the optical path. A cloth shroud assists with this.
3. Mirror cooling.
4. Collimation.
If you pay attention to to the above, a truss tube should be at least as good as a solid tube and from what I have seen is generally better due to improved control of tube currents and better mirror ventilation.
BTW, I have found it much easier to fit mirror boundary layer fans to a square mirror box as opposed to a round solid tube.
Cheers,
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