IMO, don't use sand bed for curing LR. I've done it, and had soo much trouble with it. First, all kinds of junk will fall from the rocks, and you don't want to get it buried in the sand. It is alot easier to siphone it out from bare bottom. Second, area of the rocks that will be in contact with sand wont get water flow that is one of paramount things in curing process, so you'll have to turn rocks often, and curing will take forever. Third, since sand is new and does not have enough bacteria that glues small particles together you'll have sand storm every time you take your rocks for cleaning, or rotating ....
In short, go barebottom.