Some friends I was talking with about traps, mentioned the fact that when doing undermine, none of them had ever been in a group that got the trap bonus, so with my trusty rogue I set out to find out why that was, as the info was not on wiki either.
Turns out the reason is its a large number to get it done, and its the mined floor area before you go down the hall to the end fight where you jump from rock to rock to avoid the heavily minded floor.
Traps Needed for each bonus , load up with thieves tools 350 to be safe hehe.
1st bonus 214 traps
2nd bonus 275 traps
3rd bonus 339 traps Ingenious bonus 30% xp got an additional 20k xp and with pot and ship bonuses a lot more. was well worth the effort, I just rogued away on traps while the party proceeded on to the end fight , and they still had to wait on me a bit.
Feel free to update this on Wiki if someone who reads this has access.