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So long as you have a process for accurate polar alignment each time you set up the other thing you need is the ability to accurately point at the same FOV each time. The secret to that is plate solving.
A plate solver can inspect an image and compare it to a sky catalog to determine exactly where the scope was pointed when the image was taken. It may need some hints to do that (e.g. the image scale and a rough idea of RA and Dec) or it may be able to work it out without hints at all - this is called blind solving.
There are a number of plate solving software packages around. Pinpoint is a well-known commercial product and a "lite" version is bundled with MaximDL. Elbrus is a free package. The Astrometry.net solver can do blind plate solving and is also free. Astrotortilla is free package based on the Astrometry.net solver.
If you have some images from a previous night you can use plate solving to determine where you need to point your scope to collect more data on the same objects. You can also use plate solving to assist with accurate pointing by slewing to your object, taking a test image, and solving it. You may find that the scope isn't pointing exactly where you thought. Sync the mount position to the result of the plate solve and slew again. Repeat if needed...
Automation software like ACP, SGPro, CCD Autopilot and CCD Commander will do all this for you and makes multi night projects a lot easier.
Cheers,
Rick.
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