It is up to you how detailed do you need / want to be your analysis.
For non critical situation, your model should be enough. If you are afraid that the real location of the support have a large influence on the results, then go ahead and add the trunnion. Compare the results and you will understand.
Sometimes, on critical systems, you may need to rotate the trunnion (90 deg, 180 deg)or to have a longer or shorter trunnion in order to reach acceptable results but this yu can not know until you actually model the trunnion.
Regards,
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Dan