Calin, sempervivums are very hardy and awfully hard to kill other than by rotting/drowning - they'll probably be fine.
Dirtdorphins, when I said "troughs are elevated above the ground surface", I meant that the soil in them is sitting above ground level, which forces drainage to occur. Troughs don't need to be sitting on blocks (if that's what it sounded like I was saying) but they can be. In cold climates, I think there may be some limit to how much air circulation one wants around the trough, so most of mine are sitting on the ground.
