I am currently contemplating a new in-ground pool. One PB is willing to give me a steel-wall, vinyl lining with sand (and only sand) under the liner. The other PB is going with concrete-wall, vinyl lining with vermiculite. My questions is the following: Is a sand-only floor base ok for an IGP? I heard of footprints/other indentations being made as people walk - is this true? In addition any pros/cons of steel-wall vs. concrete-wall (I am in NY). The pool would be a 20 x 42 kidney shape. Thanks.