I would highly recommend Lumicon for OAG -
http://www.telescope-service.com/Lum...t/Lumicon.html
Not only consider a motorised focuser, consider a motorised, PC controllable one with a temperature sensor. My logic here is:
1. A steel tube will shrink as the temperature falls, so you will need to compensate to maintain focus as temperature varies (which is why I love Carbon Fibre tubes - almost no thermal expansion / contraction)
2. Focusing with say a Bathinov mask - or any focusing - I don't like to touch the tube at all - I want it rock steady and for folk to not even walk by it when I am focusing or imaging! So PC controlled is great!
3. If the tube has a read out of both its position and temperature then you should be able to chart and match temperatures to position.
4. If you use eventually use a mono camera and filters - then (not sure is this was refractors only or SCTs too) each filter will focus to a different position - so its handy tracking where each colour focuses at any given temperature.
Quite a few folk here use Moonlite focusers - they are exceptional quality and look great too!
http://www.focuser.com/storefront.shtml
The Moonlite focusers with High resolution Stepper motors, temperature sensing and Variable speed mini controllers (hand operated or USB controller v2) work very well!
http://www.focuser.com/cgi-bin/dman....cgi&category=5
PS
The Astrodon MMOAG plus fittings is around the same price as the ONAG
http://www.innovationsforesight.com/...On_axis_guider review here
http://www.cloudynights.com/item.php?item_id=2706