Cassini's division is indeed 0.69 arcsec at its widest point as seen from earth, though with the rings tilted on a shallow angle, if you can see it following around much of the ring plane then you are certainly seeing a dark band considerably smaller than this, possibly 0.2 arc seconds wide. And as Alex indicated its a good test of small scopes.
+1 insulating your mak will stop the internal tube current, so its ready for use from setup. Keeping the heat in the OTA also means the corrector will not cool quickly, so it stays dew-free for much longer (quite possibly all night) - and without the need for a heater.
I use a homemade plastic dewcap that extends back over much of the OTA see
https://www.cloudynights.com/topic/6...tube-currents/ though at a pinch even corrugated cardboard, foam plastic, foam rubber or a picnic rug work fine. Experimentation indicates its not necessary to cover the entire OTA nor the back, and IMHO there is some merit in leaving the back exposed.
Same applies to SCTs by the way.
Simple engineering consideration of the thermal issues imply that thin-walled dark metallic tubes are about the worst possible choice (Meade, Celestron, take heed). Carbon fibre isn't much better as it is thermally conductive - and black. A good coat of white paint does make a difference - and is why refractors were traditionally white - and likewise telescope domes.