I tried a trap out this Saturday.
I first sat on the roof, and observed how/where the bees were going in and out of the hive.
I found 3 openings, 2 of them I was able to close fairly easy. Hole number 3 was suddenly the main entrance/exit. I installed a reverse funnel and put a Nuc box near the old entry point of the hive.
Then I waited. Bees kept coming out, but there was no "pile-up" of bees returning to get back into the hive. I climbed of the ladder and saw why:
I showed the homeowner that this gap was so large, and probably had other wholes leading to the same cavity, that I gave up this fight. I am not a general constructor.
Even though i didn't want to charge anything (no cure no pay) i was tipped generously by the home owner.