Do you ever hit the bottom or is it endless
And just based on chance rather youre going to hit
Another trap door or not?

Well, technically we don't know if there is a limit, but I currently have the record afaik with 16 consecutive TDs --> lvl 55 fighting mobs over lvl 100 in solo xD

Nic has told me he's been down 15 in the past as well.

It's random but ofc you have better chance to find a TD in a bigger cata >:)