"Matthew Ota"
My guess is about 36 inches, minimum. But you do not have much of a
choice if you buy a prefab dome.

If the slit is narrow, an automated dome would fit the bill! A computer
controlled system could be devised to keep the telescope cantered in the
slit. An automated GOTO telescope would suite such a system at added
expense. Unless you have a motorized dome that can be controlled from the
observing position your going to get very annoyed, having to jump up and
turn the dome every few minutes.
Ed