I always use egg crate on the bottom to help prevent the tip of a rock accumulating alot of pressure and cracking the bottom of the tank...
Think 100 pounds of rock in a 100g tank stacked up... thats alot of weight said:
if this is why you want it cheryl, i really like how i did it turned out. I stole Sanjays idea from Next wave where he showed us how he put the rocks that formed the base and touched the bottom of the tank on square concrete stepping stones which gave it a solid flat surface to sit on the glass. worked like a champ and the bottom rocks are not going anywhere.