Ye Olde Inn

Searching for secret doors in a corridor will reveal any, whether they are visible or not.
"Zargon then discloses any secret doors located in the room or corridor you are in".
This text isn't included in the trap search rules. Does the same principle apply or are only visible traps placed?

This query arose in Q8 of RotDM. Southern double corridor standing behind the statue next to the central room. The monster isn't visible so a search is allowed. The secret door isn't visible but a search would reveal it. The trap also isn't visible. Would a search reveal it?

I would judge the position you describe behind the statue to be part of the single corridor, so no search of the double corridor should be possible, in my opinion. However, to address your point, let's consider that the entire double corridor were to be shifted downward one square so that the square behind the statue is definitely in the double corridor. I'd then say yes, the same search principle applies to both secret doors and traps.

"You must first verbally declare your search. . . . Zargon will then tell you which squares, if any, have traps." Which squares belongs to what search area? I think the answer is found in the first paragraph of the Search For Traps action: ". . . They [the four kinds of traps] can be found in both rooms and corridors. . . ." In the Quest 8 example, this concerns the contents of the double corridor, visible or not. Perhaps I'd reconsider this if the Hero stood behind a blocked square tile rather than a statue. But as it is, I think a statue shouldn't prevent looking down a corridor the same way a monster doesn't.

My understanding is that traps and secret doors do not require strict Line of Sight. Thus, a figure (even a statue) does not impeded visibility of anything beyond it, unless the specific quest so states. (I haven’t yet gotten through RotDM, so can’t comment on that specific instance as to what is going on there.)

So a statue, which normally does not block visibility, even if cutting off movement past it, does not prevent a Hero from spotting a trap beyond the statue. (The exception being if the quest says that it does block visibility.)