Can I suggest a sand box.Picture a drawer.Make a shallow one with mitre corners for finish look.3/4" sided ply works very good.Put a bottom.Attach everything with glue and nailgun.Create one floating shelve,by cutting a slightly undersized plywood the size of the box minus 1/8" overall.
You could go with double compartments.One holds sand the second on top holding a bicycle innertube a little under inflated.Your spikes go on the bottom.
Best of luck
George
You could go with double compartments.One holds sand the second on top holding a bicycle innertube a little under inflated.Your spikes go on the bottom.
Best of luck
George