Hi Markus,
You're on the right track. The darker the skies, the better. Good transparency really helps too (not so much dust, smog, junk to look through). Spend a good amount of time getting dark adapted eyes. Spend around 15 minutes just looking at the galaxies - it's amazing how much more you see after 15 minutes. Revisit the object over many nights, your mind builds up a memory bank of detail you've previously seen and you suddenly notice something you hadn't seen before.
12" should be plenty enough to pull out some detail. You should see some elongation along with the bright core. I could spot the elongation in M65/66 with my 4" scope. Also, look for the larger, fainter galaxy nearby (NGC 3628) - they make a great triplet.
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