An apparatus including a first member, a second member and a cross member. The first member has an upper end, a lower end, and a non-slip surface along at least a portion of an inner surface of the first member. The second member has an upper end, a lower end, and a non-slip surface along at least a portion of an inner surface of the second member. The cross member extends from the first member to the second member and retains the first member and the second member at a fixed distance relative to one another.
