Yes, for CCD camera work you need to find out what kind of in travel is required. I have measured my eyepieces (about 12 of them, misc varieties - Naglers, Panoptics, Plossls, Orthos,) and found that .35" in-travel was sufficient. Barlow lenses add another thing to consider. Best to measure your stuff if possible, then leave a bit more for margin (and future additions). You can always move the mirror forward later, if necessary.
Since I strive for the minimum diagonal size, I don't like to extend the focal plane more than necessary.
This is all just another good reason for building your own scope, you can configure it for your needs and change it later if desired.
Bob