Kudos for being overly cautious. Hopefully, you stay that way.
As far as there being a positive 'clunk' when you're set I don't think there is one when the trailer is positively attached. I believe it's pretty much verified by sight. There's usually a lever that stands vertically on the yoke but that won't be able to snap horizontal unless the ball is properly in the socket. Other types have a big knob you tighten on the ball. That starts out all loosey goosey and tightens up as you turn clockwise. All it's doing is pushing a metal plate in place 'under' the bottom part of the ball so the trailer yoke can't pop out. Again, this action is no good if you don't observe that it's tightly cinched up. Eyeballing it is the first step.
So I think you're doing good by giving it a good visual check several times. Cranking it up to check for ball capture by lifting the tow vehicle is a great way to check too...if fact it's probably the most used method.