That's a pretty good description of what my PCs had to deal with. The place was pretty much honey-combed with secret passages and objects that the Kobolds could hide in.
In fact at one point the PCs chased a couple of them up a set of stairs into a tower only to find a room at the top full of barrels. So it became a game of wac-a-mole or wac-a-Kobold as the case may be.
They finally got tired of trying to find the Kobolds and ended up rolling the very barrels the Kobolds were hiding in. Granted, it was a dizzying bumpy ride for the Kobolds, but by the time the PCs realized that the barrel they rolled down the stairs had the Kobolds in it and got back down the stairs, the Kobolds had fled into their secret passage network.
But yeah, the best way to play them is to use their prep of the surrounding terrain! Oh, and these Kobolds were not leveled either and the as the PCs watched the keep burn, a couple of them noticed quite a few Kobolds escaping out a tunnel, a couple hundred yards away at the edge of the forest.