Since SSD drives are very light, it would be sufficient to use two screws in a 3.5" or 5.5" bay on one side of the drive only, preferably on the side that faces the cover, of course. They weigh only about two to four ounces and screws on one side will easily support their weight. Make sure that both screws are securely tightened but don't overtighten them until the point they break or get stripped. Use two or three fingers on the screwdriver and apply a secure torque.
But, no matter how you install it, don't let it loose in the chassis. Chances are that it will mechanically damage or electrically short your motherboard, resulting in its immediate death.